I started early December and still made it before beginning of May (though English is not my mother tongue, and I generally read and learn slowly…) with CFAI books. I highly recommend studying from this source - apart from known argument that eventually it’s Institute that prepares the exams, I would add you can’t get such a comprehensive, consistent picture with well structured information while reading materials from other providers (I used one of them at level II and failed twice, then switched to CFAI for good). Not to mention, I assume you will miss some very interesting stories like that of Enron swap ‘trick’, or the emerging markets expansion, or Pascal’s wager…

Also much knowledge that can be useful some time later in your professional career.
Then, last full month I did CFAI mocks and AM sessions from previous years, and Schweser’s QBank and Practice Exams (and these, I must admit, are REALLY worth working with.. good job from Schweser! - I had mine from 2011 from a friend who passed one year before), but I still refered ONLY to CFAI materials when it comes to my reviews.
So, to sum up, you have more time than you need - just don’t waste it - to study efficiently from CFAI books. I’m sure you won’t regret your time invested in reading the books from Institute instead of some more condensed volumes from external providers.
And one more advice if you decide to take it… Always PRAY to God and ask him to send the Holy Spirit to enlighten you during the exam. No joke. Each time I went to church or prayed at home I told Him how much I want to pass, how important it is to me, how much I depend on Him and His grace! Then (after the exam) I prayed that my Grader(s) are not so severe on me, that they are healthy and happy in their lives, and I did it for over 2 months (and I will still do!). It works, I tell you - it must have been a true miracle that I got 6/9 >70% and passed despite the fact I didn’t even start 2/9 essays??!!

)) Good luck!