Not much in the way of leaning because the roped walkway is in the immediate back of the section, so the wall you could lean on is part of the walkway. Standing in the back of the section, no problem, but all you would have at your back is a non-supportive rope. You could ask the CM if you could enter the walkway to lean on the wall (explain your bad knees/back) during the show and see what they say. I don't know if it is a fire code/etc. that they have to keep these clear. The answer might be cast member dependent.
We were front row, so I stood and leaned against the front rail until we were asked to be seated by a CM prior to show start.
We had plenty of room to stretch out our legs, so if you had family to help with the getting up and down, you should be OK (cushion helps).