You can apply for the 60 days now. Costs 3,900 baht. Different IO's require different documentation, but it's nothing difficult - you do not need an embassy letter just the usual things e.g. photo, proof of address & passport copies. UK and US embassies are not issuing embassy letters anymore:   https://th.usembassy.gov/covid-19-faq/) Last update; October 13, 2020: "non-Thai nationals can visit any Thai Immigration office to request a 60-day extension of stay.  Thai Immig