How do I extend my visa for 60 days based on marriage in Bangkok and what documents do I need?

You wouldn't be applying for a 60 day "marriage extension" because there's no such thing 😮

You'd be applying for a 60 day "visit thai family" extension and your thai family just happens to be your thai wife 😛

IF you're here on a 60 day free stamp entry, OR a 30 day extension from a free stamp entry in Bangkok you'd go to IT Square Laksi Plaza for the 60 day visit thai family extension.

Keep in mind unlike the 30 day extension based on tourism which starts the day your current stamp runs out, once you get an extension for a different reason (visiting thai family) it would start the day you apply and if you went early you'd lose all those days on your current stamp.

You need a TM30, marriage certificates, wife's thai i/d, house book listing, copies of the data page of your passport, your entry stamp, your 30 day extension (if you have one) a filled out TM7 application for extension along with a passport sized photo. Those things along with 1900 baht will get you the 'visit thai family" extension (and as you pointed out, your wife <- the reason you can even get this extension) has to be with you as well 🙂