Steelcase Amia vs Steelcase Gesture

It is way too stiff and the bottom part does not have enough cushioning. My back and bottom started hurting after several days of using this chair. At first the swiveling, non-lockable arm rests did not bother me, but soon became a pain in that they always move, even when I'm sitting down working. The chair is heavy to move, so you have to move it from the back support, and not the arms as they will swivel and move

I'm only 5ft 10in so I doubt I should be feeling an open area behind my rear while sitting on this chair. My next issue also involves the base. It rocks back and forth by about 1/5 of an inch. I'm not sure if that's a conscious design decision but it's annoying when I try to re-position myself in the chair