CFBOOKA

Third party books are a good bet, if you can afford the extra cash. The blog has an offers page that you can try some samples or get discounts.

The CFA Institute material is sufficient for the knowledge and is the de facto source.

Depending on your experience/education, it may or may not be the most efficient route to study. My friend Ben wrote a blog post on his tips for an efficient study method.

In addition, the examples in the books are probably not enough practice. The last 1-1.5 months should include LOTS of practice doing mock exams.

At Passed Tense we also recommend practice after each chapter and then practicing again a few weeks later to ensure retention. Our Passed Tense Adapt Exam Engine was designed to provide both the full exam practice and the need for regular topical quizzes.

the CFA books are more than enough! It is more a matter of if you have time to go through all that material or if you learn better from a different modality (videos, flash cards, etc…)
I have only ever used one 3rd party provider, Schweser, and it worked for me. They offer the Schweser notes which are a condensed version of the CFA texts and a multitude of other study materials.
Take a cruise through the other articles/threads on here and you will find lots of guidance on this topic.