My understanding and what I plan to do is arrive and get 30 day visa but have flexible ticket to leave before end of 30 days. (You’re ticket needs to show you will depart before visa expires I believe) Apply for 30 extension (maybe longer if needed) and then change flexible flight ticket. I have accommodation arranged for my full stay however long. You will need to put accommodation address on visa.
I am a uk resident double vaccinated.
Singapore, Etihad and Emirates do flexible ticketing. Qatar used to show as flexible and I think they still are but you’d need to check. You need to book with travel agent company that will allow use of flexible ticket. Check with travel agent first. Booking directly with airline automatically gives you flexible ticket. At present you will still need $100000 covid insurance coverage.
You should probably wait for the Thailand pass system to be announced as there will be changes. This is supposed to start on November 1st