Husband (the hunter) says that it was a kind of stadium seat. I'm not finding the one we had on Google (and we don't have it anymore, so I can't check the label), but that this one (http://tinyurl.com/yj4nj2w
) is pretty close. The important part is the EPS filling-he says that as long as it has that, it'll work. It's not pressure sensitive (I thought it was), just very, very good at reflecting your body heat back to you.
I think we paid <$20 for our, although that was several years ago. Try Walmart, Bass Pro, Dicks-any sports store with a hunting section ought to have something that would work, especially this time of year!