I flew last Sunday with Eva Air direct to LHR from Bangkok. No medical needed, brilliant service. I shall be flying with them in future after Emirates let me down so badly. Enjoy your self quarantine!
If you’re thinking of retiring here, why not spend 6 months or so travelling around, living in one place for a month (cheaper option than shorter stays). This will allow you to experience the location, figure out the prices and the possibility of meeting others. Thailand is a big Country, and as different as say, Brighton and Basingstoke!
If borders are still closed, I can’t really see any option but to extend. Incidentally, my UK Travel Agents have just told me that Emirates intends to start flying again in June.
I’m number two hundred and forty something in the “have Embassy letter” priority queue. I hear there is going to be one Thai Immigration officer there. I’m going, but do the math. Pretty sure a lot of people are going to come away disappointed.