I agree with zowie. Especially if you're riding a lot (12 miles a day qualifies), a harder seat is better than a soft one. On a soft seat, your bones sink in allowing the seat to press on all your soft bits. On a hard seat, all the pressure is on your bones. It means you'll probably have two sore spots (one on each side) for a short while until you get used to it, but you'll notice the improvement immediately.

Many many factory seats are very poor for riding extensively, because soft seats feel great on the test ride.

That being said however, seat adjustment is also very important. Check out sheldon brown's website (www.sheldonbrown.com I think), he's got some good articles on seat adjustment and what can be causing all sorts of discomfort.