I think you attach the cushion to any bouncer chair, or use it on its own.
We had a wedge, which had a harness on it to try and get ds on an angle steep enough to help his reflux. I would pay anything to have found something which would help his reflux.
Unfortunately he was completely unable to hold his head up for a very long time when on his front, and would just scream blue murder if 'tummy time' was attempted.