Krabi you can fly directly into from BKK on TG. Its about a 45 minute flight from BKK. Then van transfer to your hotel, which should be minimal, depending on where you stay. If you go for Koh Lanta. You would fly to Krabi, then take a 45 minute van ride to the ferry terminal. You can arrange a speed boat from here through your hotel to take the 30 minute boat speed boat ride. At the Layana they bring you right onto the beach at the hotel. The owners are typically there to greet you. Its a nice arrive.

If the weather is bad or you choose not to do the speed boat option, your van gets on the car ferry. Short trip across to the island, then another 45 minutes driving, depending on where you are staying on Koh Lanta.

Good luck.