Can I extend my 60-day tourist visa in Thailand up to 6 months, or should I switch to an Education Visa for a longer stay?

I'm shutting this down. ALL Extension of stays are 1,900 THB, and all visas are 2K THB (or in equivalent local currency). Filing a 90 day report is free. If you do not file a 90 day report, the fine is 2K THB the next time you do something at immigration.

It is possible to get a ED visa "above the table". To learn Thai, talk to some Thai language schools, like Duke Language in Bangkok, but you can only stay for one year. You can also get a bachelors or masters degree, which will let you stay for the length of the program.

nope, not possible. You entered on a 60 day tourist visa and you can apply for a 'regular' 30 day extension ONCE.

If they still offer 60 day covid extensions you might be able to get one of those BUT the program is set to run out on May 29th <- meaning that's the last day you can apply for one