Laterider,
I think when you have an injury like yours it's a good idea to find an instructor who can work with you one-on-one. They'll be able to show you how to adapt exercises so as to avoid aggravating your injury and start building towards being able to do the exercises that are probably in your book.
There are a lot of Pilates teacher training programs out there. You'll want to look for a teacher who has had 600+ hours of training, and if you can, someone who has experience with your type of injury.
I have a bias for classical Pilates. As I understand it, there are also "modern" Pilates programs that are very good as well, but I don't have any experience with them. The classical repertoire has served me well. I am going on 4 years since I fractured my S1-S2.
You can find a lot of classical Pilates instructors
here
or otherwise ask around in studios in your area. You should be able to find out what kind of training the teachers have done, how much experience they have, whether they have experience or interest in working with your injury. You may even find someone with a PT background, which would probably be ideal.
And short of that, I've found the
Pilates Connections forum to be a good place to look for information. You might try posting your questions about modifications for your injury and pelvic floor sag there. But keep in mind you can only learn so much from reading a book or looking at a forum, and at some point it really helps to have an experienced person show you how to do the exercises with the proper form.