Don't know what your supplement plan is . Medicare Plan C is a private company of your choice. Some plan C cover limited care for tourists in other countries.
I had problems with the address drop boxes and I was told to use the same sub as I used for the district. It doesn't let me continue until it gets what it wants. Try all the options till you get the right one. 555
Go to Thailand Embassy site and find what kind of visa you want, E-visa is online. Non- immigrant- O. or OA might be the way for you (just a guess), Do from outside Thailand.
Google flights will send you an alert. Try the explore and look at the map. BKK is normally the lowest cost destination for me, but??? Train, short hop air, experience the journey