Safest bet would be to use a border run service. They’ll take you to the border and make sure you get back in. You should be okay to fly out and back in, just make sure you have the three proofs…onward travel, accommodation and 20k baht or equivalent in cash. Immigration are asking more questions of people doing back to back visa exempt entries. Things work a bit different in Thailand than Europe! METV is another option.
Just wait until closer to the time. Nobody knows what the rules will be next week far less December. Could still be 60+30, it could revert back to 30+30, or you do 30+30+border run or tourist visa. Who knows, you’ll get your time one way or another 🙂
I suggest you follow Brandon's advice on obtaining a non-O before travelling to Thailand. Then apply for a one year extension of stay, make sure you obtain a re-entry permit and you can come and go as you please during the validity of the extension. A non-OA is valid for one year, if you buy another years insurance you can extend just before the visa expires getting you basically two years out of it. Then you're done. You apply for visas using the Thailand e-visa website.
What exactly are your plans, how long do you actually intend on staying in Thailand? The more info you give the better the advice member can give regarding options. I note a couple of days ago you were promoting Mexico as an easier option to Thailand🤔