Just noticing an update on the London E visa application website and the London Thai Embassy website.
I believe they may no longer issue a single entry Non O visa for retirement UNLESS you are in receipt of a state pension or at least of state pension age, which means you need to be over 65 years old.
That now is the only choice. The other options for retirement, apart from the O-A visa, have gone. I would suggest anybody not over 65 years old (The minimum state pension age) and wanting to apply for the Non O visa for retirement, calls the Embassy and asks if it is still possible to apply before wasting your time applying.