Ali -- I breastfed and I don't think it affected mine in a negative way. I think it has more to do with gaining/losing weight, not nursing. I'm such an oddball, I didn't gain any weight with either of my babies. Nada. 'Course, I was on a diabetic diet, and that helped.
I have gained quite a bit since, though... (sigh)
I gotta say, I'm a BF advocate...give it a shot, it is SO much easier. And just because you had no luck last time, doesn't mean you won't now. My first didn't want anything to do with it, but my second was a champ.
And since I haven't said it yet, Congratulations!
Um, maybe I won't be you just now, after all.