I recently passed the CSSLP exam and utilized the following sources as prep materials.
1. CSSLP Certification "All in One" Exam Guide 2nd edition.
2. The Official Guide to the CSSLP CBK 2nd edition.
3. The CSSLP course from Plural Sight (Kevin Henry).
4. The CSSLP course from Cybrary (Kelly Handerhan).
5. Viewed various Youtube Videos discussing "baking" security into the SDLC.
I also have experience with software development and with management of the software development life cycle.
Many congratulations! I hope to join the CSSLP ranks at some point in the future too.