I would seriously consider getting a new seatpost that allows angle adjustment. I've also found that tiny angle adjustments make a huge difference in comfort with Brooks. Very counterintuitively it's often a slight angle up. For me that allows you to not slide forward and put pressure where you don't want it.

I ended up picking up a salsa seat post http://salsacycles.com/components/shaft_seatpost/ that allows you to adjust angle separately because it was such a pain getting it just right with my old one.