During the 60 odd years I was involved with flight instruction and its associated issues I have probably used and recommended many of the available texts for use in our business.
One thing that has always stood out as primary and something a lot of instructors miss is that whatever text you choose that text should be understandable not only to you as an instructor but as well to your students as it is quite natural that your students will gravitate to whatever sources you use personally.
Along these lines one soon sees that texts such as Aerodynamics for Naval Aviators (one of my personal go-to books BTW) might not be the best choice for your student to go out and purchase. :-))
The old standbys like Kershner are fine as are many other available texts but after looking them all over closely and using many I have to say that above all of them I have come to appreciate the books available from Rod Machado. His books are excellent and for the average student written in language easily understood and retained.
I will freely admit that Rod is a personal friend but I would never recommend anyone as a competent source for aviation material who I believed not to be worthy of that recommendation.
Your choice of course but my vote for you as a new CFI would be to seriously look into what Rod has available.
Dudley Henriques