Very Simple.
Take a train from Bangkok to Surat Thani (it would be better if you take the evening train 7.30 pm, from the Hua Lamphong). Air conditioned Upper-Lower sleeper will be just fine for this journey as it is very comfortable.
It also saves money as the ticket is only around (upper 750, lower 850 per person) THB.
The journey is around of 11-12 hour.
You will reach at Surat Thani by 7.30 am. Beside the Surat Thani train station you can get Seatran or Lomprayah ferry packages that is very good & cheap too & convenient (450 THB per person). The package consists of bus from Surat Thani to ferry station & the ferry cost too from Donsak Pier to Nathong Pier at Koh Samui. The bus journey is of 1.30 hour to 2 hour. Lomprayah Ferry is faster, which will take less than an hour. Seatran ferry is big and comparatively slower, which may take around 2 hours.
You will also get drop services from the Ferry Station to hotel at Koh Samui which will take extra cost. If you want to go by local transport, it is also available and comparatively cheaper.
Edited: 9 years ago