Goody makes boar bristle brushes for people and their prices tend to be reasonable - maybe this? If you feel the bristles are too hard for your dog, know that you can get a softer natural bristle in a baby brush. If cost isn't an issue with you, Kent makes some of the best natural bristle brushes around, most beauty supply places carry their line. I've also seen natural bristle brushes (for people), specifically the small oval shaped ones meant for men with short hair in the 99 cent store, this might be a good way to go since it'll fit in your hand well.
Hope this helps,
Penny