Train to Chumphon then boat[edit]
A good option for travelling from Bangkok is to book Sleeper Train #85; leaving Bangkok around 19:30 and arriving in Chumphon at 04:00 and then have a ticket booked for the 07:00 ferry. Most ferry operators can pick you up from the station where you can while away the 3 hour connection gap. You can also buy your ferry ticket at the station when you get off the train at 04:00.
Bus to Chumphon then boat[edit]
Lomprayah have an inclusive ticket from Bangkok on a comfortable large bus included in the price with connections to the port.