Is the problem the B17 or getting the positioning to be upright on the bike? I'm 270 and find the B17 works for me on a pretty upright position.... I use swept back bars and high stem. I know saddles are very personal...so just sharing what works for me.
I also would second the observation that once you get beyond a certain distance (say 5 - 8 miles someplace) bike specific clothing makes a huge difference in overall comfort.....
Any way here is a pic of my set up in case it helps
