IMO best to get extended travel insurance for that period of time. Here (and maybe many places) get you 2 ways. No coverage for any pre existing as well as “common illnesses” in your age group. Likely the best you will get is coverage for catastrophic injury caused be accident. Consider putting aside a great deal of money as your backup in needing medical care. That way if nothing happens you still have it. Good luck
Google is your friend and so is the local Thai Embassy. You don't need an agent just follow instructions. If you can not follow the instructions, stay home