So if I extend my TR visa for 30 days on September 6th, I could switch that visa to covid extension for another 60 days on September 25 and get the 60 days extra from Sept 25?
I just needed the free certificate provided by hotel that I had completed my stay with all my negative tests, (not the 700thb one). They looked at that at check in, and they also gave me a QR Code that I had to scan that takes you to a health form you need to complete before arrival. Filling out that form generates another QR code that they scan.
Boarded off the plane, they scan your QR code after you get off the tarmac, then you're free to get your bags and leave.
I know you're not looking to fly but I did just that yesterday and it was so straightforward. 39 minute flight, out of Samui airport within like, 10 minutes of landing. Mostly the delay was because the baggage conveyor belt got jammed.