I’m actually going to go through this line by line - not to pick on you OP but because there will be a tonne of women reading this feeling just like you and as an older woman it might be useful to one or more of them.
“It’s not fair in my son”: what’s not fair on your son? That his grandma doesn’t get a gift from your nephew bought and wrapped by you, stressing you out, resenting his dad, feeling miserable? Think about what you’re saying here. Apply some logic. And even if one Christmas when you’re 9 months pregnant with his sibling your son doesn’t to benefit from a perfect (according to you but almost certainly not according to him, because he’s a child) Christmas…what’s going to happen to him? Seriously? Do you think he might feel a little disappointment (he won’t)? And so what? What will happen to him if he does? Do you accept this is about you, not your son?
He deserves a clean and warm home: ok, sure. Switch the heating on. Tell your DH to do some cleaning.
Presents nicely wrapped under the tree: so buy some, wrap them (doesn’t have to be nice, he won’t give a shit), and put them there. Fine.
Lovely home cooked Christmas dinner: you’re 9 months pregnant. This is not necessary. Christmas dinner of some sort is fine. Tell your DH to pull his finger out and sort it out. M&S if need be - again, you’re 9 months pregnant. Why not insist on doing it standing on one leg?
This is his childhood: yessss, and? Will it all amount to nothing if 25/12/25 isn’t the picture you have in your mind? Will you have failed at mothering, failed at Christmas?
This is about standards which I am not dropping: ok, stop moaning then. Do all the things, and stop complaining if this is about your standards and you won’t drop them. I guarantee neither your DH nor your son could give a shit as long as there’s food and gifts. You can’t have it both ways. They’re your standards, you do the work. If you set standards for me and complained I’m not meeting them I’d tell you where to shove your standards.
The thought of turning up to someone’s house….physically sick: so take a bottle of wine. Not difficult. Hardly warrants a complaint.
Wish it was that simple: IT IS THAT SIMPLE. DONT DO IT.
It'll be me they talk about behind my back: and? You’re martyring yourself at 9 months pg in order to avoid bitching by people who would actually bitch about a 9 month of woman not doing enough for them?
Just. Stop. You are spoiling the very thing you’re looking for with this martyrdom. It’s your own fault. Stop doing it, stop complaining, stop feeling resentful. It’s really, really easy.