which is completely irrelevant to both the poster's question and to Canadian immigration. That said, 99% of expat jobs in Thailand have shit pay. Furthermore, there's no way you could afford your expat retirement lifestyle in Thailand after a Thai career.
You can apply for an other extension, which will cost you another 1900 baht. This is a common practice. They will refuse your application but give you 5 extra days to leave the country.
in my opinion, Bangkok or Phuket have nothing to do with this. It's the time required between the initial step of the sale and the final step of the sale. What you do afterwards is irrelevant to this process. How about this: you put your house with an agency, go to Thailand, begin the process to get your retirement visa, or apply for a multiple entry tourist visa, wait for the agent to call you, fly back to sign papers, return to Thailand, wait for the final step of the process, fly back to the UK, and then return. Sounds like you have a pension... This should be an easy process that only requires a few moves. Your worries are probably more associated with the "move"... I'm a life long gypsy and lived in 7 different countries... Trust me, it's easier than you think, wherever you decide to go.