hey davie and julie
seems we arrive at the same day in BKK. Who knows, maybe we are sitting in the same train when we get down to Huahin :p
For Thailand I never book in advance. But thats a personal thing for each person. There are lots of travel agencies and you can just book the bus the day before you go and then it will be ok i think.
For accomodation in HH i recommend:
www.jinningbeachguesthouse.com
Nice and always very friendly staff.
If you have question you can contact me via private message.