I had the 2005 LX which has equally bad seats.
My back has never been in so much pain after driving any car before. Avoid this car if you are tall and suffer back problems.
I drive a new 2005 Mk2 Focus Zetec Climate and find the seats very comfortable and I'm 6' 2" and 220lbs.
I recently replaced my mk1 Focus LX with a Renault Megane solely on comfort grounds. The Focus was a great car - reliable, well made, fun to drive and cheap to run, but the seats were criminally bad. I'm 6ft 2 and "amply proportioned", but my brother in law is 5ft7 and 11 stone, and he complained bitterly about the seats after driving the car for just an hour. No upper back support whatsoever, plank like base units and the total lack of lateral support are little short of criminal in this day and age.
It sounds like the mk2 hasn't been the improvement I would have hoped for. Glad I didn't hold out and test drive one. The Megane might not be as much of a drivers car, but I am more comfortable after 4 hours in it than I was after 20 minutes in the Focus.
I have a South African made mk2 Ford Focus CL. I'm 5ft 10 and the seating position is just perfect for me. Its more comfortable than my parents Mazda 3. On the other hand, my mother who's 5ft 2 finds the front seats uncomfortable because the under leg support is too long for her. So I reckon a test drive is required before buying it.
Regarding seats. If you do so much driving I would change your car. I find the seats in my VW (Mk IV) hard, but supportive. Or better than a German car would be a Saab.
If any body needs lumber back support (like I do) then forget the Focus, It's a great little car, but the seats are the poorest I've ever sat in. I've done a measly 15,000 in 3 years in my Mark 1 Focus and that's more than enough. The mark 2 I tried this week is marginally better, but still very poor, the back support is far to low down, it's your back that needs support not your back side.