Dependent on how much height and firmness you need.. I bought a very firm pad that was to go onto the seat for my mother's wheelchair. It was just enough to help her on the soft chair that she was worried about plus we took that thing and used it in alot of chairs and situations.
It might be especially nice if you opt to do an outdoor chair and need the padding.
I agree with @Layla
and did the same for both of my hip surgeries. I rented an electric lift chair and used it almost constantly, slept in it, ate dinner in it, watched tv and chatted with friends, while all cozy in it.
It was some sort of vinyl so it could be disinfected , then when it arrived, I draped a nice large quilt over it.
The medical supply store had two men deliver it and set it up It was a real love affair between me and that chair, then one day I looked at it and decided it wasn't needed any longer so called the delivery people and had it picked up.