for a short term visa you need to have a flight booked to leave Thailand within the validity of the visa. However this could be a £20 flight to malaysia or somewhere and then just don’t show up. This is simply to just get the visa
stv is 90 days and can extend twice but now they have put an expiry date on that visa and it will stopped being used at the end of September I believe. 60 day visa isn’t an stv it’s a TR tourist visa and can extend by 30 days to give you 90 days in total
you need to send documents but can just be screenshots of a flight itinerary showing the flight numbers etc. And then can book a hotel on agoda where it’s pay at property, get the confirmation and then cancel