I have found book jewellery (also referred to as "book thongs", but the term "thong" conjures disgusting images for me, and, the synonyms are negative) to be much better than a traditional bookmark. They're unobtrusive and easier to use. I love them and want to provide them with at least 1/2 of my books. My next purchase of bookmaking material will render me almost 400 books. It'll take me forever to paint the covers and so I won't order/make the jewellery all at once. Plus, I can only buy them gradually anyway. I should've had many more by now but bills got in the way. Bleh. I am going to try cowrie shell book jewellery but I doubt the shells will be heavy enough for the cord I'd use. Well, we'll see.
I'm working on some books for a gallery in Toronto.
I've decided to keep books at 3 sizes after I run out of my material: 4x6, 5x7 and 5.5x8.5.