What documents are required to switch from a Non-Imm B visa to a COVID visa in Thailand?

You’ll need this stuff. Not all offices have the same requirements so it may be slightly different depending on which of the 70+ offices you use.

A copy of your passport data page (signed),

A passport photo,

Proof of filing a TM30,

A copy of your departure card (TM6) (signed)

A copy of your latest entry stamp (signed)

A copy of any previous Covid extension stamps (signed) (Phuket requires this other offices may not)

In Phuket they require the copies to be in portrait not landscape. This means the top of your passport aligns along the shorter side of the A4. Except for the Data Page where most passports are “sideways”

(Other offices may not be as pedantic)

A filled out TM7 (application form for extensions) - the form doesn’t have a space for your email or phone number but just write it on the back (page 2).

A filled out STM2 (acknowledgement that you understand the rules for overstaying)

A filled out “I don’t want to leave because of Covid form” - I have no idea if it has an official name or number.

And 1,900 baht.

The forms are available at your local office. Most have places on site or nearby that can do the copies and photos.

Many offices will give you a “under consideration” stamp requiring you to return somewhere from 5-14 days later where they will stamp for the remaining 60 days. If they do you MUST use the same office to “close out” that stamp. For example you cannot get a “under consideration” stamp from Bangkok and close that out in Chiang Mai 15 days later.

I believe IF you're on a Non-B visa EXTENSION you're going to have to cancel that before you apply for the covid extension by taking documents from your employer stating you don't work there AND proof that you cancelled your work permit ONCE you get the extension based on employment cancelled you can then apply for a 60 day covid extension.

You only need photocopies of the passport, stamp of the last entry to the country, the last visa, TM6 and 1 photo. 1900 thb. at the office they give you the form to write. Nothing more. I did that yesterday in phuket

Typically all you have to bring next to your passport (+ copies of its relevant pages) and a picture is a current TM.30 (proof your current address being reported). The actual forms required vary by immigration office - but will be handed to you there. Some IO additionally ask for a letter of your embassy or an email of that embassy stating that they are not issuing such letters. For exact current requirements in Phuket - maybe someone else here knows more details.

Which immigration office are you planning to use?