I believe the OP asked if anyone had tried a kneeler -- one of those
reversible thingies like

I try to do all the weeding by bending from the waist. My back doesn't mind
that. If I want to be on my knees, the garden kneeler is a godsend. It gives
my poor knees a pad and it makes it easy to get up. Otherwise I kind of flop
around trying to get my knees to lift me.

Marilyn in Ohio