How can my partner and I extend our holiday visa in Samui for an additional 30 days?

There is no such thing as a holiday visa!

Most offices allow you to apply for a 30 day extension when you have 30 days or less left on your current stamp

Some offices allow you to apply for a 30 day extension when you have 45 days or less left on your current stamp (Chiang Mai, Bangkok, Buriram, Samut Prakan)

BUT

A couple offices only allow you to apply for a 30 day extension when you have a week or less left on your current stamp (Samui, Jomtien)

There is no reason to wait for your stamp to run down as you don't lose any time applying early the 30 days is added to your current expiration date

This is a general list of what's required to get a 30 day extension on a free 60 day visa exempt OR a real 60 day tourist visa entry

Doubt you're here on any visa at all 😮 Most likely you showed up here and got stamped in free for 60 days on what's called a "visa exempt" entry

There are OVER 80 immigration offices in thailand so saying where you are is super helpful