What documents do I need to extend my Non Imm O (Thai Spouse) Visa in Chiang Rai?

You need to have proof of relationship if you want to apply for 60 day visiting Thai family extension. General information is here, but check with your local immigration office. You can, but don't have to wait until the last minute because the extension will be added to your current stamp

Umm, you're getting a 60 day visit thai family extension so you're going to need to have all the marriage documents, copies of your wifes thai i/d and house book listing, AND you take your wife with you <- seeing as she's the reason you are getting the 60 day extension

You can go when you have 30 days or less left on your current 90 day entry stamp.

Just curious are you hear on a single entry Non-O visa or a year-long multi-entry one? I ask because if it's a year long multi-entry you can just go to the border, stamp out of thailand, stamp in and out of Lao, turn around and stamp back into thailand for another 90 day entry stamp