I had the same issue as you devans. I tried EVERYTHING.
you need to get a seat with an airbag, otherwise you will have no insurance in the event of an accident.
Recaro make these (overseas) and are VERY expensive. I was even told that if i wanted to fork out the Dollars to get one across it may still be rejected by insurance in the case of an accident.
As others have said you may want to go to look at an automotive trimmer to help.
I tried this... TWICE....
The first attemmpt was to add extra foam and create a good shape to the seat. This didnt work - it actually made it worse.
Second attempt saw a different trimmer remove all the first guys work and add a Recaro "Air Lumbar Support" This is a product that can have air pumped into it or removed to create the ideal support.
Again, this didnt help. After many hours of labour I had gotten nowhere
I was fed up of having back problems (as Im a rep and do LOTS of driving) so i decided to trade the car in and get back into an Australian built sedan.
Now I have my FG XR8 and i couldnt be happier.
Oh I might add that the headrest angle is TERRIBLE in the Foz.
The FG Falcon still pokes out a lot further than older cars, but I have been told this is the new design for current model cars (something to do with preventing serious neck/back issues in the event of a crash)
Even thought the headrest on the falcon still sticks out, its nowhere near as bad as the Fozzy was.
I think the designer of the new gen seats at subaru should be fired!!!!
without a doubt the ONLY thing that upset me was the seat and it enforced me to lose even more money and trade in to a different car.
I wish you all the luck in the world trying to find a solution mate. Good luck