I breastfeed my daughter till now and she is going to be 2 years old next Friday! I really enjoyed this special bonding with my daughter. During this 2 years I had received lots and lots of critisms/comments from friends, families and even strangers! (worse after she turned one) I was so hurt and cried for many times and even thought about giving up. However, I am glad that I have supports from my husband, LLL leaders and mothers who are breastfeeding.
My MIL was very supportive as she breastfed her children too, but my father once asked my not to breastfeed in the public because "police will arrest you as it is not decent to do so in the public!!" I said "first of all, there is no such thing, second, if the police really want to arrest me, go ahead, nothing can stop me from nursing my hungry and crying child, I am her mother!"
Some said "your daughter is slim/petite" I said "yes she is not fat, has good size (her weight and height are always within chart) and doctor said that's because I am not fat and she got that from me" or "good for her, easier to find husband"
Some said "it is bad to breastfeed toddler, etc" I said "WHO recommended to breastfeed till 2 years old" or "look at my daughter, she has good skin, fit, not fat, active, happy, confident, has good appetite, healthy, why is it bad for my child?
Some said "formula is better than breastmilk" I said "you got the info from advertisement who wanted your money and I got my info from thorough research/books/websites" Free things do not mean less good (air is free, sunshine is free, moonlight is free, wind is free, mountains are free, tree and flowers are free, birds flying in the sky is free, happiness is free...)
I have never made any comments about people giving formula to their children (formula is not cow milk, infant cannot drink cow milk until 1 years old). It is the parents' choice. All parents want the best for their children. If a parent think formula is good for their children, they do what they like. If a parent think breastfmilk is good for their children, leave them alone!
I truly understand your problem because I have gone through it myself. It was hard but once you are used to those comments, you will become thick face like me

You have to be prepared to face those situation (being critised in the public) and have a few answers ready (LLL website has article about how to face critism) Be confident, and smile to people who are so "kind" to offer you "advise". When you say "I have done my thorough research/WHO said/my doctor said..." people tend to shut up immediately as they don't know anything and have no proof of what they said.
Do what is best for you and your child. Most of all, enjoy it!