First of all, you need not to step into the tub while holding the book in your hands. It becomes very difficult to get into a relaxed position while holding the book. So, it is imperative that you place the book at a safe place, from where you can pick it after sitting in the tub.
Keeping the water level slightly low is very good, but it may cut down the pleasure of sitting in the warm water. Therefore, the best option is to make something for the book to sit on.
You can get a piece of Plexiglas. Make sure it is long enough to be on top of your tub. Place the glass near your face, making sure that any body movement does not disturb the water.
Another thing that needs to be kept in mind is to avoid getting your hands wet. For this, you should always use a dry washcloth to turn on the bath faucet.
If you don’t rely on the thermometer, use your feet to determine whether it is the right temperature. However, if you have to use the hands, don’t forget to dry them before holding the book.
In order to avoid water touching your hands, you should use the outside rim of the bathtub to step in. If you are using a glass slider, the book must already be on that. Make sure the slider is resting on the foot of your tub.
After getting into a relaxed position, slide the glass towards you. Make sure you don’t move it too quickly, because the book may slip down into water.