Quick update - applied for my non-imm O visa by post to the London Thai embassy on last Tuesday and received my passport back with visa on Saturday morning. I included 3 months bank statements but no flight booking and paid by cash. Thanks for all the comments! π
Last time I applied by post I paid by postal order but this time I sent cash. I'm not sure if the website has been updated since I last applied but it currently says that application by post must be paid by cash or postal order. Hopefully should be ok...