If you arrive before the 25th you can get a covid extension up to 60 days aswell so you should be able to enter on 30 days and then get that for 90 days total
I have been in Phuket almost 2 months I came on a visa exemption for 30 days and extended it for another 30 days.
Our flight got canceled on the last day our visa runs out so we went to the immigration in Phuket and they are currently offering up to 60 visa extension for everyone asking because of covid this has to be done before the 25th jan.
I haven’t got a onward ticket before but I just paid for a ticket to Singapore which I made sure I could get refunded. Only thing I didn’t get full refund only 80% but this way I found was easy to do.
Also I wasn’t asked upon arrival in Thailand for my ticket only before I left the county I was currently in (Dubai) but they didn’t check just asked if I had a onward flight
My airline (Etihad airways) asked at check in and I said I did have a onward flight but they did not check it. I just purchased a cheap flight that I need to cancel, also wasn’t checked when I arrived in Bangkok.