Beginner: Should I switch to a less advanced samatha practice?

... The issue is that I don't have a true teacher per se, but a collection of resources which offer diverging guidance. ...

Samatha practice it is advisable to have a teacher as quite a few things can go wrong without proper guidance. In case of Vipassana the chances are that few things will go wrong as long as you practice right. In this case you should be careful if you understood and practicing the technique right. Also you should have enough theoretical knowledge to navigate any issues which might popup.

... I began doing 10-minute sessions using the ... app ...

I am not sure if apps can help in meditation other than for ties and occasional chies to keep you mindful. I would be very weary about commercial apps or courses.

... after relaxing and breathing naturally ...

You have calm the bodily fabrications as per the Suttas

See:

• How is the Pali Phase "Sabbakayapatisamvedi Assasissami... passasissamiti sikkhati..." Interpreted as per Different Linage?
• How does one calm one's bodily fabrications?
• page 35, Knowing and Seeing, 4th Edition, by Pa-Auk Tawya Sayadaw

... focusing on the space between oneself and external objects ...

This paragraph sounds like the space Kasina. This type of meditation (Bhavana) is best done under a guidance of a teacher. For more information see: page 66, Knowing and Seeing, 4th Edition, by Ven. Pa-Auk Tawya Sayadaw. One famous Samatha master is Pa-Auk Tawya Sayadaw. Perhaps you can do a retreat at his monastery or under a student teacher.

... more compassionate person ...

Perhaps you can try developing sublime attitudes (loving-kindness or benevolence or friendliness, compassion, empathetic joy, equanimity)

Should I switch gears to another, less advanced samatha practice now, or stay on my current path?

This you have to decide. Best is to get a teacher especially if you want to do Samatha. Try World Buddhist Directory or http://www.paaukforestmonastery.org/.

Alternatively, I could test out the other methods for a bit. But which one?

You can also try: https://www.dhamma.org/en/index, http://www.internationalmeditationcentre.org/global/index.html.

"merging the mind with space"

This sounds like trying to emulate a formless jhana. To attain the formless jhanas before the form jhanas is unstable and advised against by Buddha. He even went so far as to say that those who do this--even attaining the 4th jhana before mastering the 1st jhana--could regress perpetually (due to bad habits).

Samatha practice is ideally breathing practice and ideally leads to the first four jhanas and their corresponding factors. Simple as that. I would recommend reading anapanasati and The Six Dharma Gates to the Sublime for more varied techniques on breathing practice--straight from orthodox Buddhism. In addition, if you have the time, I would suggest reading Master Huai-Chin Nan's material.

Below is an excerpt that may help put emphasis on the right things:

When sitting in meditation the mind becomes refined, but whatever state it's in we should try to be aware of it, to know it. Mental activity is there together with tranquillity. There is vitakka. Vitakka is the action of bringing the mind to the theme of contemplation. If there is not much mindfulness, there will be not much vitakka.

Then vicāra, the contemplation around that theme, follows. Various weak mental impressions may arise from time to time, but our self-awareness is the important thing; whatever may be happening we know it continuously. As we go deeper we are constantly aware of the state of our meditation, knowing whether or not the mind is firmly established. Thus, both concentration and awareness are present.

To have a peaceful mind does not mean that there's nothing happening; mental impressions do arise. For instance, when we talk about the first level of absorption, we say it has five factors. Along with vitakka and vicāra, pīti (rapture) arises with the theme of contemplation and then sukha (happiness). These four things all lie together in the mind established in tranquillity. They are as one state.

The fifth factor is ekaggatā or one-pointedness. You may wonder how there can be one-pointedness when there are all these other factors as well. This is because they all become unified on that foundation of tranquility. Together they are called a state of samādhi. They are not everyday states of mind, they are factors of absorption.

There are these five characteristics, but they do not disturb the basic tranquility. There is vitakka, but it does not disturb the mind; vicāra, rapture and happiness arise but do not disturb the mind. The mind is therefore as one with these factors. The first level of absorption is like this.

We don't have to call it first jhāna, second jhāna, third jhāna and so on, let's just call it 'a peaceful mind.' As the mind becomes progressively calmer it will dispense with vitakka and vicāra, leaving only rapture and happiness. Why does the mind discard vitakka and vicāra? This is because, as the mind becomes more refined, the activities of vitakka and vicāra are too coarse to remain. At this stage, as the mind leaves off vitakka and vicāra, feelings of great rapture can arise, tears may gush out.

But as the samādhi deepens rapture, too, is discarded, leaving only happiness and one-pointedness, until finally even happiness goes and the mind reaches its greatest refinement. There are only equanimity and one-pointedness, all else has been left behind. The mind stands unmoving.

Once the mind is peaceful this can happen. You don't have to think a lot about it, it just happens by itself when the causal factors are ripe. This is called the energy of a peaceful mind. In this state the mind is not drowsy; the five hindrances, sense desire, aversion, restlessness, dullness and doubt, have all fled.

But if mental energy is still not strong and mindfulness weak, there will occasionally arise intruding mental impressions. The mind is peaceful, but it's as if there's a 'cloudiness' within the calm. It's not a normal sort of drowsiness though; some impressions will manifest - maybe we'll hear a sound or see a dog or something. It's not really clear, but it's not a dream either. This is because these five factors have become unbalanced and weak.

The mind tends to play tricks within these levels of tranquility. 'Imagery' will sometimes arise when the mind is in this state, through any of the senses, and the meditator may not be able to tell exactly what is happening. ''Am I sleeping? No. Is it a dream? No, it's not a dream...'' These impressions arise from a middling sort of tranquillity; but if the mind is truly calm and clear, we don't doubt the various mental impressions or imagery which arise. Questions like, ''Did I drift off then? Was I sleeping? Did I get lost?...'' don't arise, for they are characteristics of a mind which is still doubting. ''Am I asleep or awake?''... Here, the mind is fuzzy. This is the mind getting lost in its moods.

It's like the moon going behind a cloud. You can still see the moon but the clouds covering it render it hazy. It's not like the moon which has emerged from behind the clouds clear, sharp and bright.

When the mind is peaceful and established firmly in mindfulness and self-awareness, there will be no doubt concerning the various phenomena which we encounter. The mind will truly be beyond the hindrances. We will clearly know everything which arises in the mind as it is. We do not doubt, because the mind is clear and bright. The mind which reaches samādhi is like this.

Ajahn Chah (1919-1992)

excerpted from A Taste of Freedom from A Collection of Dhammatalks by Ajahn Chah

I know exactly how you feel. I am 6 years+ and still feel the same confusion. So many contradicting opinions out there about what is correct and what is incorrect then others say there is no such thing as incorrect meditation. We are told constantly to not just listen blindly to the Buddha or the teacher but try it for ourselves but then when we feel we aren't progressing and feel confused and ask questions we're told that its because we're craving or expecting too much etc!! Well no actually we are just trying to figure out where we are going wrong or right but not getting any clear answers.

This sounds really caught up in all kinds of cravings for spiritual attainments. If this 'craving' is dropped, the path the Buddha taught, which is the abandonment of craving (rather than mental gymnastics & magical formulas) might be learned. Samatha & vipassana are natural fruits of the properly established or collected mind - aka samadhi. The Buddha taught:

What is the faculty of concentration (samadhi)? There is the case where a noble disciple, making 'letting go' his meditation object, attains concentration, attains singleness of mind. SN 48.10

As for the practises mentioned in the original post, they are not 'advanced'. The more complicated & willful they sound, the less advanced they are. The most 'advanced' practises are the most simple. That is why the statement: "Do nothing" often frightens people. Simply 'let go'.