I don't have children, Herbert1234. Long story but I made that decision when I was about 11 or 12 because I didn't want any child of mine to endure the same miserable childhood that I'd had. I regret that now but it's too late.
My DSis is 17 years younger than me. She won first prize in the scapegoat lottery when she was still in the womb (I know this for a fact). When she was born, I fed her, changed her, hugged her, sang to her, told her bedtime stories, taught her the alphabet etc. We've always been close because of that and it's always irked my mother because of that, even though M has no interest in DSis whatsoever. Never once has M ever hugged my DSis or me. As children, we'd try to hug her but we might as well have hugged the ironing board.
DSis was braver than me. She has two lovely children but struggles to be a good mum because, let's be honest, our mother is not exactly a role model. I absolutely adore my little nieces. This is key to what I'm going to tell you next.
DSis has always been low contact with M because it's as much as she could bear. However, like you, she felt it important to give her girls contact with their grandparents so she gritted her teeth for their sake. My viper of a mother would open her arms wide and cry "my angels" and my little nieces would run to her for a hug. And all the while, my DSis would stand there in utter misery as our mother gave every impression of being a loving mother and grandmother. All a sham.
When I went NC with my mother, she couldn't get to me, even though she tried. However - remember how I said I adore my little nieces? - she realised she could get to me through them. She began treating them with casual coldness and contempt. My little nieces didn't understand why their grandmother had suddenly turned on them. It was intended to bring me to heel. My DSis realised this straight away. Now hell would freeze over before she would allow her girls into their grandmother's orbit again.
Please think about your little boy. He is an innocent child and deserves love and cuddles and affection. However, to your mother, he is just a tool. She will shower what appears to be affection on him while it is useful to her to do so. As soon as he shows some personality of his own, or whenever it becomes expedient to upset him as a means of hurting you and making you comply, she will do it.
I'm sorry to say this to you. It's hard to hear about your own mother. However, you are a mother and it's your job first and foremost to protect your little boy from harm. 