that's what I mean get your extra 30 days on January 3rd. Then go in on 25th January for your 60 days covid extension. (You can get your covid extension a few days early from when your +30 expires). It's confusing I know... But your Visa timings are very good for the Covid Extension on the 25th January.
Your timing with Visa's is perfect to claim the 60 days Covid Extension on the 25th of January. Take your +30 for the TR now and go to immigration around the 25th of January to get the Covid Extension +60 days. (As of now the Covid Extension finishes on the 25th January).
Pick up a burner onward ticket for piece of mind. It's the Gatekeepers at Airline check-in that present the most risk about not letting you board. I am a habitual repeat offender when it comes to not buying RTN tickets - but I did use a burner ticket for Sandbox this time.
TrueMove month to month is 300bht with unlimited data and calls. 10mb/second speed as a Hotspot. Very happy with it used for 4 months now, renew every month. Pick one up at TryMove store or 7-11.
Yes documentation. I printed out everything. The burner ticket was $10usd. The burner tix was with Singapore Airlines as well - I'd don't know if she looked up my details on that flight or just 'eyeballed' the ticket/paper.
I used one to come here in August- it worked a treat to satiate the Goons at Singapore Airlines check-in; Who just follow a script and ask for your return flight. In other words without that, I'd prolly still be back in Melbourne.
I did what you want to do from Australia and prepared everything for the 90 days. Including; Insurance, fake burner ticket home after 90 days, 76 days 'reserved' accommodation (not paid for)- after the 14 days Sandbox. You could go this route OR prep everything for just the 60 days and then extend in-country and change your flight (as Stuart mentioned).