D.H.
For the sake of your marriage and to show your husband that you are part of a team, you MUST tell your mother to stop with the comments to your husband or she will not be welcomed to visit. PERIOD. Put yourself in his shoes and you understand how lucky you are that he hasn't told her himself. It is YOUR mother and YOU have to do it (or she'll just make it about him). YOU are a mother now and your #1 concern is for your family, which includes the happy home of you and your husband. Your child needs his father and you need your husband. Honestly, mothers have to come second now.
I think it is great that she wants to visit, but she has to realize that you and your husband are the parents and you work as a team. When she puts him down, she is putting YOU down too. I hate confrontations, too, but I am willing to do anything to protect my marriage and my children. YOU CAN DO IT, TOO!!! I hope you make some changes before she hurts your great partnership. Your son is counting on it! Good Luck