"Carrying is supposed to be comforting, not comfortable." But beyond that you may want to revisit how/where you carry in order to address the chair/car seat issue.
I'm going to go ahead and guess that you carry somewhere between 4:30 and 5:30. Lots of folks do. But then lots of folks cannot easily access their handgun when sitting down.
For some custom-work $$ you can get someone to put loops with snaps on your holster (yes, it can be done to kydex - even OWB kydex) so you can reposition the holster as you transition between postures.
Or you could permanently relocate your holster to somewhere closer to 3:00.
Or you could learn to sit differently.
Putting rubber baby buggy bumpers on your mags will just slow down the chewing up process, and maybe leave rubber marks where they rub. I'm surprized you had not considered Houge or other brands of rubber grips for the 1911 the way you did for the magazines. Not that bumpers are bad, but I just don't see them fixing your concerns.
So many choices.