The third choice that I suggested was go to a vegan place. The idea of being vegan is really foreign for Thais. What am I trying to say is that you might have to be in those big cities like Bangkok, Chiang Mai, or Phuket. With these big cities you might still have to put in some work to find "a vegan shop". But it's not impossible. Personally, I think the idea of J food matches vegan ideas, more than vegetarian ones, because J and vegan are almost the same, except J's use of oyster sauce.
The last point of this article is that Thailand is great for vegetable and fruit lovers. However, there are only a small number of vegetarian/vegan dishes that are real authentic Thai. Most dishes in recent times are fusion dishes which is good because it serves the current purpose of life. So it doesn't matter if is authentic or not, as long as the diet you choose fits with your health system and your life purpose. Hope this article was helpful.