Can people who don’t believe, yet don’t not believe in Jesus Christ, still make it into heaven if they’re a good person?

I'm going to ignore the very wishy-washy "don't not believe" bit for a moment to just address "Can people who don’t believe [...] still make it into heaven if they’re a good person?". And the answer to that is:

No

No one is a "good person". No one (Romans 3:10-12). "All have sinned and fall short of the glory of God" (Romans 3:23). You will not gain Heaven through works: "no one comes to the Father except through [Jesus]" (John 14:6).

I realize there are probably some folks that consider themselves Christian out there that will disagree, but IMO, the Bible is pretty clear on this subject. We are saved by grace alone.

All have sinned. All are born sinful, and are incapable of saving themselves... and yet, Christ died for all sin, no matter how heinous, and this is a free gift.

If you stop and think about it, this is also an excellent logical argument for Christianity being true. Christianity is, as far as I know, the only religion in which you can do absolutely nothing to "earn" salvation, and in which salvation has already been earned for you, and by God himself! This is contrary to Man's logic, which is why in every religion created by Man, one must do something to be saved. That makes sense to us, but "the word of the cross is folly to [unbelievers]" (1 Corinthians 1:18).

I might also add that those who believe in Sola Gratia consider it fundamental to Christian doctrine. Why? If you think about it, to deny Sola Gratia is to deny Christ. In order to say that "being good" is necessary for salvation, you must say either that Christ's death was insufficient, which is to lessen God, or worse, unnecessary. The theme of the entire scripture is that Christ, both true Man and true God, came not merely to be a good example, but to bring Salvation. If, therefore, you deny that Christ's death was necessary, you might want to seriously consider why you call yourself Christian. If you deny that it was sufficient, you call Him a liar, because on the cross he tells us "it is finished" (John 19:30; another possible translation is "it is accomplished"). Not "I've done my part, now it's up to you". Christ Himself tells us clearly that his death is sufficient.

Moreover, why in Heaven would you want to believe in anything else? If you believe you must do something to "earn" Salvation, how can you ever know that you have done so? What a horrifying thought! Thanks be to God that we need do no such thing!

To more directly address some of the points you raise:

I’m a good person.

You are not a good person. (I'm not a good person. Your pastor is not a good person. No one is a good person.) You are a sinner in need of Christ's forgiveness, and thanks be to God that he forgives you!

I don’t not believe it him, but I can’t say I’m a whole-hearted believer. I’m sent to hell for simply not being 100% sure?

Be careful here, because this may be verging into works righteousness... and thank God for that! If salvation were dependent on our having absolute faith, I'm pretty sure we'd all be doomed. "Lord, I believe; help my unbelief!" (Mark 9:24)

I guess this is what you mean by "don't not believe". Your boyfriend might be more Christian than he realizes. How does one not obtain Grace? Well, one can obviously not know it is available (here we could get sidetracked into a whole other debate of the eternal fate of those that never heard of Christ), or one can reject the gift. Feeling uncertain is natural; I believe there are very few, if an, Christians who have not felt doubt on at least some occasions. For most, it is a constant struggle, but take comfort knowing that salvation is a gift that does not depend on anything you can do. On your own, you cannot even accept this gift, but it is the Spirit working through you which calls us to faith. Therefore, do not despair, neither let your heart be troubled, when the adversary and your own fallen nature causes you to doubt. Instead, I would commend you and your boyfriend to remain in the Church and in the Word. Surround yourselves with others that you may know God's love and know that you are not alone in your struggles.

You also had some interesting thoughts on the nature of heaven that aren't really on topic. I would encourage you to ask a separate question!