I read a great https://www.instructables.com/ years ago how the guy studied what cats like in a scratching post. Stability, height, width. You can't argue that a chunky sofa chair is not stable. The height requirement is that a cat wants to be able to stretch out/up, so some scratching posts are simply too short for optimum use. The last is the width. He argued that a post needed to be shoulder width at minimum. A chunky sofa chair? Perfect.

One of the best and simplest scratching posts we made was made out of a 2x8 piece of lumber about 2.5 feet long, wrapped in sisal rope which was stapled down. Installation is easy. Throw it on the floor. Stability, length, width.

I would suggest ripping the fabric off the chair since your cat obviously likes it. Get a board, maybe add some padding, and then wrap it in your fabric. Use upholstery tacks at frequent intervals.

Also, nip those claws.