Do I need to provide proof of a 65,000 baht monthly deposit for a retirement visa in Thailand?

First of all, you have to check with your local immigration office whether they accept 65K monthly deposit method for an extension based on retirement.

If the embassy of your passport nation in Thailand issues an affidavit, you need only that for financial proof.

In case your embassy doesn't issue affidavits (US, UK, and AU are among them)

1. A 65K monthly international transfer method can be used only for a 1-year extension for the second year or later. You cannot use the monthly deposit method for the initial in-country Non-O visa based on retirement or the first yearly extension for retirement.

2. You need more than 12 months of international transfer, at least 65K per month, as of application day for a one-year extension based on retirement.

3. If you applied for a yearly extension using banked money of 800K baht, you have to keep 800K for three months after an extension is approved and no less than 400K baht for the rest of the year until you get approved for next year extension regardless you do monthly transfers of 65K.

If you mean switching 2 to 3, you must keep BOTH for a year when transitioning.

Attached is a rough image of how to switch the financial proof methods. It may or may not help..