Hello,
I sought some advice a few days ago and based on that, visited the Songkhla immigration today, to do a 60 day extension based on a family visit using a Non-O visa. Also to note, my current entry stamp was due to expire on the 19th of April. We successfully got the extension.
Below is the full list of required documents for the Songkhla immigration.
* The Visa Extension Form (TM.7) + 1 recent passport size photo. This form will be given to you upon arrival.
* Your passport and a signed copy.
* A copy of your current visa page, signed.
* A copy of TM.6 arrival card, signed.
* Your wife's house book (tabien baan) and a signed copy by your wife.
* Your wife's ID card and a signed copy by your wife.
* Your marriage certificate and a signed copy by your wife and yourself.
* An updated Khor Ror 2 form (unsure of how out of date this can be, ours was 3 years out of date). You can obtain this fairly quickly at your local Amphoe office for 10 baht.
* A google map from the immigration office to your residence.
* A family photo (selfie of you and your wife basically). The immigration also took a picture of my wife and I together.
* 1900 baht fee for the extension itself.