Browsing through Pinterest the other day I noticed a pattern for a crochet corner bookmark, so I thought I'd give it a go.
I used the recommended yarn and hook and it was fun and quick to make but I'm not that impressed with it.
I think it's a bit bulky, although you are able to close the book okay. My opinion would be that it would be better made in a thinner yarn.
If you fancy making one there are various designs on Pinterest and they don't take much yarn.