What documents do I need to renew my retirement extension at Bangkok Immigration using the 65k Baht monthly deposit?

As well as your bank book showing the 12 x 65k Baht foreign transfers, you do also need to have a letter from your bank which lists all the relevant foreign transfers. Advisable also to get the bank to rubber stamp (immigration loves rubber stamps).

You'll also need your insurance certificate, even though it's in their database. Make sure it covers the full 12 month extension period.

I think you need a couple of photos as usual and the form. Bring your most recent 90-day report and TM30 receipt (may not be necessary, but doesn't hurt to have it). I also take my current condo lease, just in case.

Just make sure the money is deposited directly into your Thai bank account from an overseas source. It can not be deposited from inside Thailand, like taking money out of an ATM and depositing it. There are no exceptions to this. You need two letters from your Thai bank. One stating that it is your account, and your name is the only one on the account. The other letter shows each monthly direct deposit coming from an overseas source for the past 12 months of at least bt65,000, with no exceptions. Both must be on your bank's letterhead. Then, copies of your bank book for the full year showing the deposits. They will also want your bank book to compare.