Upvote:5
Yes, legally speaking, you need a visa:
Foreigners entering Thailand are not permitted to work, regardless of their type of visa, unless they are granted a work permit. Those who intend to work in Thailand must hold the correct type of visa to be eligible to apply for a work permit.
And as you've figured out, you can't get one as a self-sponsored online entrepreneur, at least short of setting up a Thai shell company with a local as director. Your options are thus:
And obligatory disclaimer: this is not legal advice, so don't blame me or Travel.SE if you end up eating c**kroach gruel at Bang Kwang Prison!