To me, you might be limiting your seat choices alot just because you want a neat storage compartment in there. You might end up sacrificing ride quality instead of getting the seat that would fit you. If you need a small compartment you can easily pick the right seat and just one of those mini accessory bags.

something like this that just hides under your bike seat (there are smaller sizes if you want):

http://www.mec.ca/Products/product_d...=1272983898356

and having the right seat that can work for you would go a long way on your cycling enjoyment.