Here's a cool and unique way to keep the place within your book! It's fairly light on filament, easy to print, and will fit on the “standard” 220x220mm build plate.

There's two different sizes and a shelve variant with both sizes to accommodate any style you are trying to fit and hold almost any size of book.

2 walls and 12% infill is plenty strong and keeps the print time low. Print in the orientation that the model loads with.