-- Last Updated: Oct-31-12 11:35 PM EST --
You found out the hard way. I also found out cotton can be dangerous even on land, when I was 19 and got caught in a very cold spring rainstorm while bicycling in jeans. First of all, the cotton clothes sag horribly when saturated. My jeans were practically falling off my hips. Second, wet cotton is actually colder than NO clothes whatsoever if there's any wind. Third, even if the sun comes out in full and you're safe on land, wet cotton takes forever to dry.
Wetsuit or drysuit, or something else--just don't paddle in cotton unless you're in a hot part of the country, in warm water. I take it you were wearing a PFD, because that helps hold some warmth to your torso.
Back to your question about practicing, you can supplement live instruction with good videos. For not much $$, those can provide really useful advice. I wouldn't rely on videos or books alone, though.
Good luck finding a pool to practice in. What I'm finding is that many municipalities are so strapped in budget that they are cutting back hours or even closing public facilities.