So as you may remember...or maybe you wiped it from your memory as I have...my old office. And then if you can even recall, the 'chair' from my office. It was actually an ottoman that I got from the thrift store for like three bucks. I then made a slipcover for it with some dollar fabric. And yeah. I used it has my 'chair' for three years. It was a horrible experience, but kept strong and kept using it. haha.
To start, I placed the cushion face down on the fabric, also face down. Cut about a 5 inch allowance around the cushion.
I got really lucky with not having to replace the cushions and a little tightening of the screws made all difference in the world with its wobbliness.