Trade the royal beach town for the island — a night train or a long scenic day connecting through Surat Thani or Chumphon.
Find a room before you go.
The overnight trains that leave Bangkok each evening pass Hua Hin late at night — board there, sleep south, and connect with the morning bus-and-ferry to Samui. Buying it as one combined ticket keeps the connections honest.

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Board a Bangkok–south sleeper as it calls at Hua Hin, arrive Phun Phin at dawn, then the joined-up bus and Donsak ferry. On Samui by midday.
Morning train to Chumphon, afternoon Lomprayah catamaran via Koh Tao and Koh Phangan — a long, lovely day of coast and islands.
Through-tickets from Hua Hin to Samui combine a southbound coach with the ferry. Fewer changes, more hours in a seat.
Step-by-step transport guides for this stretch of the Gulf coast.