1x passport photo, copy of passport front page, copy of Visa, copy of entry stamp & 1900bht fee. Bangkok offices normally allow you to extend immediately, some provincial officials won’t extend until 14 days are left.
Extension @1900bht from an immigration office gives you an additional 30 days. Overstay is 500bht a day & is in my opinion unwise as your liable for arrest & deportation if your stopped.
METV (from your home country)will give you 9 months if timed correctly & extended. following up with a SETV from a neighbouring country extended will give you 12 months stay.
Virtually every twat there all using an ‘agent’ to provide accommodation & forwarding tickets & having to slip 200bht in their passport at immigration as proof of funds. My observations. If your a legitimate Tourist you can obtain a TV anywhere.