You'd be much better off getting an air ride suspension seat from the likes of National, in my opinion.
http://www.industrialseats.com/product.asp?pID=240&pgrID=87&categoryID=23Or, you could go nuts and get one of these and add heat, massage, etc. I really like these bad boys:
http://www.seat-specialists.com/products/knoedler-extreme-lowrider.htmlOr if you want the whole package in one easy deal, this might be your answer:
http://www.suburbanseats.com/p-national-medium-duty-prem-2tone-tan-leather-gmc-pair.aspx?catid=221 (This is the route we're going to take, most likely (but for a Ford, of course)).