In my experience, people put too much emphasis on wigs. Of course you want the hairstyle that you prefer, but at the end of the day it's just a wig. There's nothing special about a doll wig. You can buy any women's wig on Amazon or Ebay or your local wig shop and it's going to fit just as well as anything that comes from the doll manufacturer.
In fact, I recommend that people go out and buy a wig or two just to mix up the look. You'll be surprised at how different the doll looks just because of the different hair. So it's an easy way to have two or three dolls for the price of one. If you have long hair that came with a doll, then try short hair. If you got blonde then try a brunette. I think you'll be surprised at how easy it is to change up the look.