The best files are made by people who have put much time and effort into creating sessions which are effective. They are not terribly expensive, and you will support and encourage the creation of more and better files. There are plenty of good free, introductory, material to be found. It really depends on what your into, what appeals to you.
But do be careful what you seek.
Once upon a time I was absolutely repulsed by the thought of wearing diapers, age play, and sissies. Now, 20 years later, I am a total diaper addict. Totally consumed by my desires and needs. Lost to my fetishes. And I've never been happier.
Hypnosis works, if you've the mind for it.