Below are two examples of book page holder. One was created using wood and the other using a 3D printer. The first project can be purchased on Amazon (https://goo.gl/KuK99a) for $26.95 cents.
This tool can be created on a 3D printer by using the files downloaded from Tinkercad.
This is a reupload of one of my first ever designs on Tinkercad. Basically you slip your thumb in the hole and place the bottom wedge in the middle where the pages meet. It's meant to hold the pages down so you can read with one hand and not have to worry about the pages coming up so much.Source: Search | Tinkercad or Amazon