There is a great brush that I'm using right now for my wigs. I don't want to be advertising a brand, but it's basically a flat brush with spike like bristles that are super soft. This is, by far, the softest and most effective wig brush I have found. It works perfect!
The combs I used before were too rigid and they would pull out several hairs from the wig every time I brushed. I also had one with round steel tips and the tips would get caught on the cap of the wig. I haven't had either of these problems with this brush. So softness is definitely the key here!