Ouch! Loaded question!! LOL I can't help
too much in the way of in-depth information but I can give you a kind of summary.
There are many different types of hair out there and probably several would be suitable for what you are looking for. Mohair is one of the most natural types of commonly used fibers for doll wigs. However it is not the easiest to work with and typically requires patience and practice to achieve polished-looking results.
Synthetic hair can be found in a TON of different types and textures and can also provide a natural look. They all have different qualities and I would suggest some research to get a better idea of which kind of hair would be closest to what you are looking for.
Hopefully somepony else will come along who can offer a bit more advice for you. Good luck!!