We are currently in koh samui having entered thailand on a single entry tourist visa which was good for 60 days. we are now at 45 days in thailand and will need another 29 days after our initial 60 days are up. Am I correct in thinking that all we need to do is go to the immigration office here in samui and we can get another 30 day extension? We have not applied for any other extensions in the past year. And does it matter at what time that we apply for the extension? Can it be done anytime and they just add the 30 days on to when our 60 expires, or must we wait til the day our 60 days expire? Thanks for any help.

Just go to immigration and get your 30 day extension. It will be 30 days more added to your current permit to stay.

You will need 1 photo, copy of your passport photo page, visa, entry/permit to stay stamps and TM6 (departure card).

Fill out a TM 7 form and pay 1900 baht. Form download: http://www.immigration.go.th/nov2004/download/pdf/tm7.pdf

Yep. Pretty painless. BTW The photo needed is a passport size one.