I've used the silicone rubber tubing that I had left over from my model aircraft making days as padding on a few different things. The tube is about 6mm across, and the bore down the middle is 1-2mm in diameter, so they work very well on hooks!

I used it as padding on some hooks when I hung an old sword up once, and it works great. It also takes ages to perish, and doesnt crack or anything. It literally lasts decades.

You can pick it up at most modelling supply stores for a couple of quid per metre IIRC.