Go to your local fabric store and look on one of their bulletin boards for someone who makes slip covers for sofas and chairs. Contact them and see if they are interested in your seat project. Alternatively, go to an auto upholstery place and see if they are interested. They may try to sell you some crap foam as part of the project so proceed accordingly. I bought Temperfoam "knock off" foam from Wicks and I think the product was called Sunmate. I got a couple different densities and built up the seats with the densest foam on the bottom.
Steve Rothert
Long-Ez N49SR