I recommend the book
If you liked this movie for reasons beyond the costumes and music, you will surely love the book.
The movie does not deviate from the general theme and plot of the novel, but as is usually the case, the original work provides a far richer treatment of the themes and a much stronger insight into the hows and whys of Orlando's lengthy journey.
The adaptation does a pretty good job of distilling Orlando to its essentials, though I probably could have done without the titles between acts and the sly looks into the camera.