@B**
yes it seems like that to me too; that’s why I chose this route.
you just need confirmation letter from your doctor with Hosptial letterhead, and an appointment letter from the Hosptial. For the letter, you can simply ask them to write you a letter for visa extension. They will do it for you.
Then make a follow up appointment.
If you have ongoing medical history in Thailand, it would be the best. I have on going treatments so it was really easy for me.