Sorry to hear that - Have you tried Recaros? Also, maybe raising your seat and getting closer to the steering wheel to flex your knees might help. Sitting low with legs fully straightened out creates a "straight leg raise" that can aggravate radiculopathy.Been there, done that, prognosis is poor. I wish I could figure out why it happens in some cars but not others. It might give me some clue how to deal with it.
That said, have you done the Pain Management/PT/Accupuncture/Weight Loss/antiinflammatory diet/everything short of surgery deal?