There has been a lot of great information here. As single, unmarried and presumably past 65yo I think it quite unwise. Not only that there are few options. One thing I'd like to point out is that when you pass it will become absolute hell for your sister to turn that home into cash in a year. She'll lose it all anyway. I can't see any benefit to owning. I would lease something and given your age and vagaries of living here for no more than 3-5 years doubly so if this is Pattaya or upcountry

8 minutes ago, Will B Good said:

This reads like an absolute horror story about to unfold.........I cannot for the life of me understand why you would buy...............renting is cheaper, safer and guarantees total flexibility.....Never buy property in Thailand. 

No issue with owning a condo. Have also bought and sold a house (marriage) with no issue, but each to their own. Personally, as a singleton, would have to have a long think. If I were seriously monied up and loved the property, might be a goer, but for peace of mind house rental or owning a condo is probably the way to go.