I have the same comfort issues with my '09, seats like flat rocks, aka "Flintstones car". No lumbar support. My 2002 ZX5 was similar and got it customized with extra padding/bolstering.
I am getting seats customized at same car interior shop for the '09, and also adding a 'pump' type lumber support device.
All 2000-11 Focus have same front seat rails, just drop in another style. Since I have side airbags in my seats, I'm not going this route, however.
If original poster could find SVT or ST seats, they would work.