Bending/creasing your book’s spine is one way to easily hold your book open.
These inexpensive gadgets can be very useful in holding your book open with one hand.
Page clips work similarly to the thumb page holder idea, but instead of you pressing your thumb to the book to hold it open you simply clip the gadgets onto the pages.
The weighted ends of this bookmark allow you to place it on your book and let it do the work of holding your book open for you.