I use a lapdesk, with beanbag fill and it works really well for some books. I just don't know how well for larger, which is why I thought maybe a beanbag proper. Just make the indentation first, before opening the book. (I'm sure there are things you can buy that libraries/museums use (I sort of recall such a thing on an archaeological show I like to watch and re-watch), but have no idea what the cost would be, or how readily available. Beanbags, however, if you can't buy them, you can make them. (Packing peanuts make good fill .. as does popped popcorn.) :)