warming up & cooling down in your asana practice are important & so is dressing in layers so that you can take them off as you build heat & add some heat when your body is done working for the time being. also, it's cold out, so layering is practically a daily requirement.!
alternative apparel (think: american apparrel without the 70's porno sales pitch) has some great thin layers in a variety of styles. the long & the short of it is that their sleeved items (read: shirts) are 25% off until 11.14.09, just enter CELN92 at checkout.