Excellent service by a well-organized company. We booked a couple of days in advance and had no issues getting from Nakhon Si Thammarat to Koh Samui. The staff at the Seatran booking counter in Nakhon Si Thammarat airport were very friendly and helpful. They checked us in and called us a van that took us on a 1 1/2 hour drive to the ferry terminal in Don Sak, Surat Thani. We waited an hour or so to board the ferry which was 1 1/2 hours of smooth sailing. The ferry has a small shop on board and the chairs are pretty comfy. We were able to take a van from the peir to our hotel in Bo Put for 150 bhat but some people paid 70, others 200, so maybe try to negotiate. Still cheaper than Grab which was an insane 660 bhat.