I'm a chiropractor and I know about lumbar support. All the ones that us chiros sell in our offices seem to push you too far away from the seat. I found a great one at the "As Seen On TV Store" for $13, and it works great in the S.
Here's one I found that is almost identical (but doesn't have a plastic buckle on the strap):
http://www.neweradist.com/product.sc...=4&productId=9
Seriously, the one I got at the TV Store is great. It gives you enough support without pushing your upper back away from the seat and it's breathable so your back stays cool.