My flight arrives Bangkok at 9am, and no flight go to Koh Samie there until evening.
Hmmm, will keep looking.
I am going to Koh Tao and meeting my son there at end of his travel tour, so I need to go straight there, no other choice.
I will get whatever transport that is fastest that i can find, and post all info i find along the way.
Bangkok to Koh Tao | Train times & tickets
The best way to travel overland from Bangkok to Koh Tao is to book a sleeper seat on a train from Bangkok to Chumphon then take a joint bus and ferry service to Koh Tao.
www.thailandtrains.com
I have done it once and highly recommend it. The AC 2nd class is more than adequate. The staff will change the seat to a bed and will wake you up just before arriving at Chumphon. The ticket is bookable on line through official site(not agent). Choice of lower/upper bunk and the AC is fierce. The New Railway Station rather than the old Hua Lamphong.
Alternatively you can catch a bus to Chumphon as soon as you arrive at BKK, stay in a hotel for few hrs before making the connection to Kho Tao.
Flight to Surat Thani is another consideration. I had travelled once from Koh Tao to Surat Thani Railway station through Lomprayah.
I hope you are not arriving just before the monthly Full Moon Party.