Iv seen a lot of pros wearing foam in there wraps and I always wondered where they got it from until I came across these on eBay check it out https://www.ebay.co.uk/itm/231960575691
Ive seen people at my gym use brass knuckle wrapped with gauze covering it for sparring. I started doing the same recently, and seriously, I havent been caught once and its actually comfortable. People who've sparred me give me respect for my power and they look a bit shocked when I punch them but they dont suspect a thing so I imagine you can get away with it in the pros.
You're better off with the winning knuckle guards. There's really no competition (at least to me.) If you want to go real cheap cut a kitchen sponge in half or toilet paper.
Even the basic Everlast or Title knuckle guard helps but some people don't like those as much.