If your document is too thick to be saddle-stitched or stapled, then perfect bound book printing is your perfect option.
Perfect Binding is a widely used soft cover book binding method. With this binding method, the pages and cover are glued together at the spine with a strong yet flexible thermal glue. The other three sides of the book are then trimmed as needed to give them clean “perfect” edges. A book can be perfect bound as long as it is 20 pages or larger. In Perfect Binding, the final page count just needs to be a multiple of 2.