I went shopping two years ago with back problems too. I had to get rid of my beautiful VW Passat TDI  because  the seats were killing me.  So I tried them all and went for long drives on bumpy roads. I bought a Kia Sorrento because  it was easy to get in and out, and the seats fit like a glove.  I had to spend more but comfort was worth it.  If your car is killing your back, it will cost you in the end.