I originally bought 4” foam and it was way to soft. Rather than play the 3 bears, looking fot the one just right, I did some digging.
Definitely, do not take the following as good advice, it is just what I did… like theowing pasta at the wall to see what sticks.
I believe I used 2” heavy density foam for the back.
I used a bit heavier density at 3” base
it was comfortable but not yet were I wanted it. I added a 1” less dense on top of that. More comfortable.
BUT I DIDNT FIT WELL.
Back to the drawing board: I upholstered the driverside differently. I used 2” of the heavy density foam rather than 3” for driver side and 1” foam for the back.
I fit better but a bit less comfy.
weight loss has improved the fit and a future tilt column will have me re-upholstering it again or finally punting and taking it into a shop