I think the B17s is just wider and less expensive, not longer. Wallingford has them listed as the same length.

You might try a men's version, but I reached the conclusion that I just could not possibly get a Brooks saddle mounted far enough back on my bike, even with a seatpost with lots of offset. I did some googling and found that this is a pretty common problem. This is actually what prompted me to realize how badly my bike fits -- we put a men's Team Pro on my road bike, and I loved everything about the saddle except that I was literally climbing off the back of it trying to get into proper position. I am going to be able to make the bike fit okay, but not with a Brooks saddle. Major bummer.