Scratching - what do your cats prefer?

Radar is pretty good with the furniture, although for a while he was going at the carpet in the doorway of the sitting room. He seems to prefer scratching horizontal rather than vertical surfaces, although he does use the scratching post.

I had the bright idea of giving him an offcut of carpet, turned upside down on the floor so that the rough side is uppermost, and it's now his favourite scratching place - problem solved, he now leaves the proper carpet alone!

He has access to cardboard which he doesn't scratch although he does like biting it (he's young and into chewing things).

I wondered if anyone had any other ideas for cheap but safe materials or objects that he might enjoy scratching on, as ideally I would like to have a few scratching spots around the flat, but can't afford and don't have room for multiple cat trees!

My cat loves the carpet...and my boxspring..she won't touch the couch..its microfibre material and it doesn't feel good on her paws I guess..thats good though, its brand new.

Plain (big) cardboard boxes get more attention than anything else, but sisal wrapped posts are a close second around here.

A two foot piece of firewood (log), laid on a sheet of plastic,an old rug or in the middle of the floor! Messy,but satisfying!

ETA- My girls love theirs!

Dusty has a board covered with carpet, and wrapped with rope. It is supposed to be a door hanger, but she prefers it flat on the floor. She even sits on it like she's going skateboarding, . Walmart, about $4.