I've got the work trousers with the knee pad inserts, but it's the actual knee bent for anything over 30 secs that hurts me, 10mins and its too much to bear and I have to roll on my side, slowly straighten my legs and gradually get off the floor with colourful language. Chopping out and soldering the big white connectors in the kick panels took me 3 days, could only do a few minutes at a time.
I've got a pit now which helps a lot on some jobs, really wanted a lift but the council wouldn't let me build the garage that high.