Uncomfortable Drivers Seat

Hello ~ I have a 2003 GMC Sierra Z71 Quad Cab and I absolutely love this truck....except for the driver's seat. It is not power and has no lumbar support. After driving it for 15 minutes or so, my lower back (spine) hurts. I don't know if one of the springs is busted or what. I bought it new (it was a demo with 5K miles) a year ago and it has always done this. Short of buying a new seat, any ideas or suggestions? Is there a TSB on this?

Thanks,
Rosscoe