Actually for the outdoorish like treehouse feel Anse Chastanet is great. I was part of a wedding party and the bride and groom stayed at Jade Mountain. Jade Mountain rooms are unbelievable and they had their own butler. You really have to see it for yourself. I stayed in Anse Chastanet and my room was great. We did have a friend who didn't like the heat, but they just moved him to a room with A/C. The road in is like a roller coaster though lol.

I definitely recommend you calling the resort to see what they can do for you as well. We had a travel agent to book everything and she was great. Also, there are so many ways to get around the island I would not worry about renting a car. The resort set us up everyday with a taxi where we needed to go. Me and my girlfriend did a boat taxi ride where she went to a shopping area in downtown Castries and I went ziplining. Really fun stuff. Made life very easy. Funny thing is a lot of the resorts came to Chastanet beach for scuba because the reef is really nice there. Oh ya, there was also a more seclusive beach. I can't remember the name but it was very quiet and the wedding happened there. Really close to the resort.

Anyplace you choose I'm sure you will have a great time in St Lucia.

I spent 3 weeks in the Caribbean and I wrote a blog with tips.
http://grenada-caribbean.blogspot.com/
The Caribbean is overrated, in my opinion.