Maybe it is best for me that I did my first extension this year and had to do all of that for the first time. But also had to show divorce decrees as well. Didn’t seem that difficult to be honest.
If you cannot find a hotel check AirBnB. They are still booking and CHEAP. We are in Ubon and planned a 1 June departure for Pattaya. Got a condo for $13 USD per night. There was one for $9 but wasn’t open for the full dates we wanted.
I did mine via Thai post. That was with the US Embassy in BKK. Not sure where you are from but if a yank it’s really easy. I did it all from the village and it took less than 2 weeks from when it left my hand until I had it back here.
Good advice above but what I would add is be sure to ask the immigration you will work with directly. I have seen that the Jomtien office requires things that the Ubon office does not. Best advice possible is go in and ask them directly what they require.