Covid Extension experience here. Arrived in October on Tourist Visa, have been on Covid extension since 25th Jan, expiring 26th March.
Went to Koh Tao immigration this morning to ask about extension, officers said no problem whatsoever, telling me to return on the 25th March to get a further 60 days (they were happy to stamp me on the spot but can only add 60 days from day applied). Also said don’t need to worry about 90 day report. No proof of onward flight needed.