I use a sleeveless kayaking wetsuit; padded butt and all!
Nice wetsuit for paddling and goofing around in the water, very very easy to get on and off. I knew this suit from using it for other activities. My swimming skills s*ck, so a draggy wetsuit wasn't going to hurt me at all.
And it only cost $105.
(mind you, when I say my swimming s*cks, I really honestly mean that. I doggie paddle and sidestroke. Took me nearly half an hour to swim 750 m.)
I got my suit from the shop that I'd rented the same kind from before. I second the idea of renting a suit if you can. Rent one for a week, train in it, try another one the next week, and so on. Kind of fun, and you'll quickly figure out what you do and don't like in a suit.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson