I love ribbons and love the idea of some scrape leather to attach the ribbon to so it slides into the opening for the spine if the Bible is hardback/leather/leather like. Might I suggest using pinking shears to cut the ribbon to help with fraying or they make something called fray check (usually located in the sewing notions)
Yin the Bible cover is beautiful
I love the look of leather bookmarks, but they are usually too thick for my books, especially if it is a paperback book (those bindings are usually glue and the pages come out easily in my experience.)