In Bangkok you can apply for a 30 day extension when you have 45 days or less left on your current stamp <- meaning you could have applied any time after Nov 29th 😮 ) so any time now
NOTE; you don't lose time going early, they add the 30 days to your current expiration date 🙂
you would go to the Immigration office located at IT Square Laksi Plaza (3rd floor) that's where visa exempt extensions are issued. It is the ONLY office you can use in Bangkok.
There are copy/photo shops next to the immigration office where you can get the required copies, passport sized photo and the forms are available at the immigration office as you enter the area.
You need proof of having a TM30 filed (notification of foreigner in residence receipt) showing you're registered as staying at an address in bangkok.
In Bangkok you can have the bank letter (and the year detail transaction report) dated up to a week before you apply for your extension. The only requirement they have is that you need to update your bank book on the day you apply
You shouldn't have an issue getting a 30 day extension on your visa exempt entry stamps
You definitely need TM30 showing you're registered at an address in Bangkok, your passport, a passport sized photo. The forms are at the immigration office that you need to fill out and there are copy/photo shops next to the location
For extensions on 60 day visa exempt entry stamps you DO NOT go to the main immigration office at the government complex on Chaengwattana Road.
You go to the IT Square Laksi Plaza immigration office on the 3rd floor.. You can make an appt to show up and be served at this website