Sharing this because housing rules abroad catch people out in ways nobody warns you about. I have been in Chiang Mai for three years, renting a one-bed for 15,000 baht a month, and only last spring did I total it up: over two years that is the price of a small studio I never owned.
The part that surprised me is legal rather than financial. Foreigners cannot own land in Thailand at all. You can own a unit in a condominium, but the law caps foreign ownership at 49% of the building's sellable area, counted per building. In the blocks everyone wants, that quota is gone long before you show up, so the first question to any agent is how much of it is left - not the price.
Second thing: a resale flat in an older building has usually been through its expensive common-area repairs, but the lifts and pumps are older and replacing them comes out of the sinking fund that owners pay into. Two buildings at the same price per square metre can be years apart on that. I compared listings by district here before deciding: https://thailand-real.estate/ - Nimman, the old city and Hang Dong are three different price levels within twenty minutes.