Your best bet is to find one with fans very far from your laptop's fan(s). Laptops pull air in from their bottom, mats pull air away from their tops. If both fans go at once, you'll probably cause the thing to run hotter.
My suggestion is just use good habits. Be sure it can always breath. If you're using it on a desk, see if you can prop it up some to give it more room to suck in air.