J.S.
I've done yoga since I was 16 (my Mom took me to classes in high school). I'm now 39, and just bought a new mat at Target - just go buy the thickest one they have. It'll cost you about $25 - maybe they'll be on sale over the holidays.
I usually bring a hand towel with me to class, if I use it on top of my mat, it helps me not slide in some of the poses.
J.