Choose CG-Lock as your first choice, and add a backfriend or a sitting partner if your existing car seat is too soft or has lousy lumbar support.
Many people get pain while driving because their back is in such bad repair that driving is the last straw. One way to tackle this is to improve the health of your back. We'd strongly recommend you evaluate and hire a Spinal Mobiliser. Using this at home for a few weeks can take years of built-up problems away from the spine, making every car seat, office seat and sofa feel more comfortable.