For your case, I would say, you should look at both male and female backpacks (as well as any unisex models). Your health, well-being and comfort should be your primary concern. And as you mentioned, your personal circumstances put you slightly farther away from the statistical median. So it is quite possible that either:
(1.) A good female backpack design could be adapted for large breasts and spare you any hassle on long treks. Breasts are delicate organs and being extra vigilant (or just too picky) by looking into as many backpack options as you can, is harmless at least.
(2.) If you however find out that a backpack designed for a male chest is comfortable enough and given its larger capacity (or any other perceived benefit over female models) is to your liking, then you should go ahead with that one.
As a personal note, and from my experience, I would like to use this opportunity and suggest:
(A.) If at all possible, try walking for 10 minutes with the chosen backpack loaded with some weight similar to your usual "payload". (e.g. borrow from a fellow hiker)
(B.) Do not go for big ("male") capacity, just because you can. Your knees will thank you, in long run, on trekking sessions longer than 3 ~ 4 hours.
(C.) Some "girly" and, generally speaking, very bright colours can improve your visibility in case of a rescue operation or wildlife encounters. This point may sound laughable in Western or Central Europe, but in Bulgaria, where I come from, few people get lost every year, to a level that a rescue operation is required. Also Bulgaria and Romania still have natural presence of European brown bear in the wild, albeit very small and (regrettably) diminishing in Bulgaria. So although the chance to encounter "dangerous" fauna close to trekking routes is very small, it is not zero. And it is a good idea for humans to appear more visible to the wildlife (not to stumble upon animals by surprise).