As a former lifeguard, I feel I am qualified to give the following advice:
- Do yourself and everyone around you a favor and do *not* get a Speedo. Those banana hammocks are a bad idea even if you're Michael Phelps.
- 100% cotton is all well and good when you need airflow, but in the pool, it's clingy, it breaks down easily, and the cotton fibers clog up the pool filters.

As a recently certified SCUBA diver, I'll vouch for wetsuits. They're GREAT. They're made to last in the water, and come in a variety of sizes. You'd probably be looking for a 1 or 2 mm thickness "shorty" suit; they are basically that old style suit, only made of wonderful, wonderful neoprene. Any thicker and you'll be dealing with the suit's bouyancy in addition to your own… and it's kind of a pain ("Though it is, on occasion, hilarous."). I recommend http://www.scubatoys.com (Henderson 2mm suits are on sale now).

Love the site, happy to help, and hope I'll have more to say in the future!