I'd read/ask on Facebook, "Thai Visa Advice" and "Thai Visa Advice - and everything else".

People are just now starting to extend their, let's call it "Quarantine Entry", or QE, first with a 30 day extension (on a Tourist Visa Extension/TVE:30+15=45 days or TR60, the STV is different, and then, after that, with a 60 day Covid Extension.

Immigration is (in some/many but not all offices) still issuing 60 day Covid extensions now out to the end of May. At some point Imm. will stop issuing 60 day Covid extensions, I think.

I guess they've changed their return ticket, or thrown it away?

I think the insurance just needs to cover the initl portion of the stay, so 45 days.

How long do you want to stay? 75 days? More details will yield better recommendations. Your passport allows for a Tourist Visa Exemption, right?

Maybe consider the TR60, which with a single 30 day extension gives you 90 days.

Getting an extension is not without challenges. Very few people are denied, but some paperwork requirements (e.g. proof of domicile/TM30) can prove vexing.