This person is talking about a letter to use for 12 monthly transfers. Multiple Bangkok Bank branches have refused to issue this anymore, and without it they cannot get their extension.
Though it's ultimately lazy immigration officers that require this. They do not want to go through the bank statement and find the 12 transfers, so they want the bank to put them all in a letter. Bangkok Bank has said they will no longer do this at some branches.
Your documents have to be authenticated by the Thai embassy in your home country and then verified by the MFA in Thailand. You'll have to get an agent to do it for you if you don't want to go back to do it yourself.
You need to bite the bullet and go to your immigration office and ask them for their handout listing the requirements. That's because each immigration office sets their own requirements, and they change from time to time. The best practice is getting their updated list every year before you will go and apply.
Once you have your actual non-O visa, then you can get a residence certificate from immigration and head to a bank. Kasikorn and SCB would be the other 2 biggest ones that foreigners choose that also have the largest limits for Wise transfers into Thailand.
You still might need to try a few branches of whichever bank you choose, as each branch manager sets their own requirements and may be more or less friendly to foreigner accounts.
Most DLT offices no longer accept yellow book for proof of residence and now require a new certificate of residence from immigration for all applications.
Each immigration office sets their own requirement.
If you cannot get the certificate of residence from Nonthaburi, you can get it from elsewhere. I got my license in Chiang Mai, where they only require a TM30 and 500 baht to get the CoR the next day. You can use a certificate of residence from anywhere in Thailand for a license renewal, though that's the address that will be on the license.
You can also try contacting FatBoys, as they help a lot of people with licenses in Bangkok, and you're practically in Bangkok