Rather than modify the workbench height, I suggest trying a bar stool or one of the kitchen step "thingys" that have 2 steps and the seat can fold up.

I have degenerative arthritus of the spine and I found that the kitchen step thingy works fine for me. When I sit, the work bench is the right height. The bench is low for standing, but I do 95%+ of my building and repairing while sitting.