Have you ever tried a reading pillow for your book? We came across the idea while perusing Montessoribyhand's Etsy shop.
Proprietress (and Montessori teacher) Meg says the Reading Pillow helps encourage a child to read. The pillow features straps to hold the book in place. It also features page holders to keep the book open. There's even a built-in bookmark. Before you run to buy one, note that Meg sells the pattern only, not the pillow itself, so you'll have to do a little work before getting a beautiful finished product.