Contact eis on here expat insurance scanners they use most companies I used Axa but use the Thai one not the U.K. one.
As for flights there are certain airlines allowed into Thailand BA isn’t one of them, Thai airways are cheap at the moment they only fly once a week on a Sunday and it’s direct at 11hrs 25mins
Axa is actually a french company but they do have offices everywhere. My one is the same as yours and everyone else’s will be also as that’s how they look, I’m a financial adviser. So they’re talking crap honestly
I’ve also just checked the U.K. Thai embassy and no such thing in there
You hand the declaration form in at the airport both in your country of departure and in Thailand but you don’t need them to be uploaded for either visa or for CoE
they can’t guarantee the next day service at the minute due to lab being too busy but they still guarantee the next one so still in time for the 72 hpurs