Funny how people think it is their right to butt into your life - especially when it's such a personal issue! Maybe just tell them that you don't feel comfortable discussing it with them and you would rather talk about something else. If they can't respect that, then walk away.
I was a breastfed baby, my older brother was raised on the bottle, and we both have good relationships with our mum. (Shane's was quite rocky for a long time, but he may be closer to her than I am now!)
I hope all works out and you get the support you need and deserve no matter what decision you make.