''ONE'' Book to get certified for PMP. With Prime Focus on getting the Certification of PMP.

The answer depends on your reading and learning style. My suggestion is to pick one of the combination below:

1) pmbok + Rita Mullcahy's exam prep ( depending when you start...pick the latest version) . In my opinion, this book is written in typical study book style with good pointer and exercises
2) pmbok + Head First PMP: A learner's companion to passing the PMP exam .This book is written in unique way.

You can review online and select from the writing style you prefer
pmbok= PMBOK Guide published by PMI (current version is 5th Edition, but 6th edition is to be released soon)

You are on right track. Too many books or references will create confusion and distraction. If stuck on a concept, it's ok to research online or watch a topic specific YouTube video etc.,

Good luck !

PMBOK + Rita Mulcahy's Book.

PMBOK & Rita Mulcahy are the best.

I actually only used the PMBOK. I might be the only member on this community that did not use Rita's book : ). So based on that consensus, I recommend solely based on my peers approval.

I had used other resources, but PMBOK as the only book.

PMBOK+PMI Exam Simplified by Aileen Ellis. I found Aileen Ellis' book helped me so much more in understanding PMBOK. I just could not get through Rita's book anymore than I could make it through PMBOK as a sole source.