Recently extended my Thailand Tourist Visa (TR) for an additional 30 days at Koh Samui immigration office. Took less than an hour and a half. Please fill out these forms in addition to this groups posted Thailand TR Visa Extension Requirements (TM30 not needed at this office). This will make the lovely lady behind the initial queue counter very happy and everyone else's life in line that much easier in turn.
TLDR : Answer Summary
The author successfully extended their Thailand Tourist Visa (TR) for an additional 30 days at the Koh Samui immigration office, noting it took less than an hour and a half. They recommend filling out specific forms in addition to those listed in the group's posted requirements and mentioned that the TM30 form was not needed at that office.