Would like to add raw bones to help keep teeth cleaner for my girls but not sure which bones are best. I do not want to feed raw, just add bones instead of using Nylabones. I don't really want them to be able to eat them as much as chew on them. I am really not sure how well one of my girls would do with bones they could chew up and eat as she has a more sensitive system. So which bones are best?