MOJO DIVERS KOH TAO
From Bangkok to you can take an overnight train from Bangkok’s Hualamphong train station all the way to Chumphon. You can check train timetables here at Seat 61 or with a travel agent. The trains are inexpensive and comfortable with a reasonable bed so long as you book in advance. Once you arrive in Chumphon it is easy to arrange a ferry ticket to Koh Tao from the station. There is a Lomprayah (ferry & bus company) office there and you can book your transfer to the pier and ferry ticket direct. A travel agent can arrange a joint train and ferry ticket.
Travel agents in Bangkok can arrange a combined ticket for a bus to Chumphon pier and ferry to Koh Tao, this is normally a little cheaper than a train ticket. There is a choice of ferry companies that operate daily services to Koh Tao from Chumphon: The Lomprayah Catamaran or the Songserm ferry operate during the day or you can catch night ferry. Check with your travel agent which one they have booked for you.