My Dad always had a negative comment about the way I did or didn't do things. I didn't have a baby/child and lived far enough away that I only saw him a few times/year. He even wanted me to load the dishwasher the way he thought was best. At first I tried explaining why I'd made that choice. For example why I chose to move to Portland. We'd end up arguing because he "knew" his way was better.
This seems to be the stage at which you're relating to these people. I suggest that you be respectful and say something like, thank you for your concern" and then change the subject. You might want to add, "I know you disagree and I'll take your comments into consideration but this is my decision."
You know that you're the one responsible for your decisions and if you are at all uncertain about one and do want to hear the other person's take on it then talk with them later when it's just the two of you. Do this only if the other person will truly exchange information and leave the decision up to you. i.e. accept whatever you decide.
Find other people with which to spend time. These people sound very toxic to me. It is never right to insist that someone else do something different than what they're doing. Well, in some circumstances there are. For me, as a police officer, I had to insist that they not break the law. lol Sounds like these people are acting like the parenting police.
The only way that they have any power over you, including power to make you feel bad, is for you to give them the power. If you're not comfortable standing your ground without feeling you have to explain yourself, then stay away from them. If these people are relatives, first try talking with them about how you feel and ask them to stop trying to convince you to do something differently. If they don't stop, tell them in a calm manner, that you love spending time with them but you'll be staying away because you don't want to listen to their comments about parenting.
If they're "friends"/acquaintances just be busy when they ask to get together. If they're true friends do the same with them as you do with your relatives.
If they're people "off the street" ignore them. For example, you're standing in line at the check out stand and the person behind you asks you a question. Answer it briefly but if they then seem want to suggest something different (argue about it) just say you don't want to discuss it.
Keep in mind that some people are truly interested in your choices and want to know more about it. I'm 67, but am still interested in parenting issues. They have drastically changed since I was in my 20's and 30's. I'm an inquisitive person who likes to understand many different things. I'm interested in change. I'm a studier of human nature. I've learned to preface my questions/remarks with a statement saying I'm only interested and don't intend to imply criticism but I have friends who just assume others know their state of mind.
I also know younger mothers who ask questions, not to be critical, but to educate themselves. They may tell you what they understand in hopes of having a two way discussion in which both people have an interest. They are open to your ideas but also want to share theirs so that they can piece the two together and make a more informed decision for themselves.
I suggest that you may feel worse after these conversations because you've allowed the conversation to reach the possibility of an argument. You don't want to argue. You want them to accept you and your decision. Thoughtful, sensitive people will back off when they sense your discomfort. Unfortunately many people are neither thoughtful or sensitive.
It will help if you accept the fact that your decision is truly your decision and you do not have to defend it so that people will accept it. Stop expecting anyone to accept your decision as being the right one for you and your child. Stop expecting anyone to have the right to cross your boundaries. Find a way to feel secure in your decision. Observe when you start to feel defensive and know that just before that point is your boundary of where you're willing to go in the conversation. Then respectfully stop the conversation before it crosses your boundary.
You will be angry. This is part of how you know where your boundary lies. It's OK to be angry. It's part of the lesson. So, don't feel guilty about your anger. If you feel guilty, the situation becomes more complicated because you have to first deal with your anger before you can deal with finding the boundary. Pay attention to know when you just barely begin to feel irritated and stop the conversation then. This will take time. Be patient with yourself.
And you may be rude when you first start stopping the conversation. That is to be expected. Again work on not feeling guilty. Then practice, with yourself, ways to end the conversation in a more respectful manner. With time you'll become so accustomed to doing this that you'll wonder why these questions/comments caused you so much difficulty earlier.