What are the steps and requirements for applying for a Non-O visa in Thailand based on marriage?

Okay, lets sort this out. You come here on the tourist visa, you apply for the in country Non-O visa for 2000baht,

It's good for 90 days,

when that runs down and your funds are seasoned in your account for 2 months you apply for the year extension for 1900baht.

IF you want to after that you get a re-entry permit that keeps your stamp 'alive' so if you came back during that year you'd get stamped in until the expiration date

That is great you legalized the marriage certificate (that means you were married to a thai in the UK). I would also go to the Amphur and file a Kor Ror 22 <- that's the document they give you to show that a thai was married abroad but the marriage is registered at the Amphur.

In Chiang Mai you need 21 days left on your current 60 day entry stamp or the 30 day extension from it to apply for an in country Non-O visa.

There is no requirement that the funds be seasoned at all in a thai bank account in your name only to apply for the initial 90 day Non-O visa.

The 2 month seasoning rule is when you apply for the yearly extension only.

Most offices want you to have the 400K baht in the account for the 2 months before you apply and then for the 30 days the year extension is under consideration (but some only require it the 2 months before)

Now to get the Non-O visa/extension based on marriage is a two step process that requires four visits to immigrations 😮

Here's how it breaks down

Visit 1 - You apply for the visa for 2000baht,

You get date to come back 20 days later

Visit 2 - you go back with your passport and receipt and they stamp a Non-O visa and a new 90 day stamp in your passport

THEN you wait until your funds are seasoned the 2 months

Visit 3 - you apply for the year extension for 1900baht

You get an under consideration stamp for 30 days

Visit 4 - when that stamp runs out you go back and get the year extension inked in