If you're looking for a quick and easy way to both bookmark a book you're reading and keep notes, use the bookmark itself.

Make a bookmark out of decorative paper or patterned cardstock so you have something pretty to look at, but make sure the other side is suitable for notes or quotations or whatever else it is you're keeping track of while reading. You could also make one with the book's cover on the front side, which is something else that would make for a good reading journal ephemera piece.

You can then hinge tape that bookmark into a reading journal or junk journal for review or more notes or reactions later on. It gives you an attractive way to fill your journals and keep track of things at the same time.