Hi, from your bungalow or at any tour desk on Ko Yao Noi you can book a Yao Noi to Lanta trip. When I was there earlier this year this was the price: Taxi + Ferry (to Tha Len pier on Krabi mainland) + Taxi + Ferry to Ko Lanta 2,300 baht for 2 pax.
Probably cheaper to catch the same taxis & ferries on your own but I would imagine it would take longer! Ferries from Thakhao pier on Yao Noi depart for Lanta several times a day. I haven't tried it myself so no idea about how long it would take.