I haven't stayed there or used it but Hub53 CoLiving are promoting discounted stays and they speak great English and would, presumably, be sympathetic to what you need to do (both of which I'd say is crucial). Personally I'd message them and see what they say.
Why not just rent a v cheap room for a couple of months? There are some incredibly low prices atm. I think it's highly unlikely you'll find someone to just 'put you down' for those, they could land themselves in a lot of trouble. Visa agent might be able to help?
have you contacted Embassy? I don’t think they are accepting retirement visas atm. But you can buy refundable/changeable ticket quite easily once you get permission. Then just a COVID test 72-48 hours before. Embassies have detailed requirements, including insurance
the problem isn’t usually on entry to Thailand, it’s being allowed to board the plane to Thailand. Although if you have a visa they don’t usually check because you usually have to have round ticket to get visa. So it’s pre checked at that stage.
You usually need a round trip ticket to get the visa in the first place (depending on where you apply). But this is all academic as no one knows what the new visa situation will be when Thailand ‘opens’.