If you are making Thailand your permanent home now, as it looks like you are doing, then be fully aware that your Medicare does not cover any medical outside of the US. Part A is free, but you are paying for Part B which is worthless outside the US. Most that made Thailand their home cancelled Medicare part B. It gives you a little over bt4000 extra on Social Security, which it sounds like you are on, or you wouldn't have Medicare.
This group can help with your citizenship.
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