Thank you!
I've driven for three days trying to adjust the amount of back support for the seat and I think I'm just about there.
Fortunately we are having a spell of warm weather so I'm also keeping the top down which is helping a lot in this last stage of recovery. Improvement has been rapid the last couple of days.
I've also looked at the big BMW and Mercedes sedans in the 2002-2006 year range and I'm just shocked the amount of car you can get for the money!
At the moment I'm just going to use proper lumbar support in the Boxster and see how it goes. I've ridden in many different sedans the past few days and it doesn't appear to make a huge difference other than ducking my head more to get in the Boxster with the top up. Stepping over the sill in a taller car is just as difficult.
Starting my back strengthening and stretching excersizes this week. Man, I'll never take my back for granted again!
I can't tell you guys how much I appreciate the suggestions and well-wishes through this difficult time, and my deepest sympathy and respect for anyone who has to go through the same thing.