I don't want to be a mother but I feel selfish for depriving my mum of grandchildren.
Why do you feel selfish about that?
Well, because I know she really wants them.
It sounds like you are doing the responsible thing. You shouldn't be a mother if you don't want to even if you feel pressure from others.
I see.
Whether or not to have kids is a huge decision, and you should not let your mom's desires play into it. You'll be the one raising a child. You should do what's best for you.