Don't stop at books about going to hospital. Remember your child will have many experiences in hospital that can be scary. Hospitals are big and strange places for kids. Everything is new so even an x-ray can seem frightening to your child. By explaining things beyond just "going to hospital" your child will be more prepared about what is going to happen.
If you aren't sure what your child will experience in hospital ask your doctor for help. Then you will know what will need to be explained. Questions like... Will my child need an x-ray? Will my child be in a private or shared room? Are all fine to ask. If it will help you explain the hospital stay to your child there's never a silly question.
Asking questions also stops you from giving too much information to your child. Sometimes to much information can be as bad as too little. If your child will not need an x-ray there's no need to explain it to them. By sticking to what their experience will be like and the questions they have you will help them a lot.