You need to separate 3 things: your actions, how you feel about those actions, and how other people feel about those actions.
You make choices. Those choices have consequences. Assuming you're someone with a rational mind and some common sense, you've probably thought long and hard about going NC with your mother and this isn't just an impulse decision based on a small disagreement. If you know this is what you have to do, you just have to go ahead and do it. You have your reasons and they are valid. This relationship with your mother is a burden on your emotional wellbeing and you're allowed to make choices in your best intrest, regardless of how other people feel about that.
You're going to feel a lot of things after you make that choice. Guilt, shame, relief maybe, sadness, grief, ... All of those feelings are normal. They are telling you that you have to process something, that you need time to heal from what has happened. Not feeling these things would make you either a psychopath or a robot, which I hope you are neither. These are normal feelings to have. They are temporary and it gets better in time. But you will carry them around in some form for the rest of your life, and that's okay. She's your mother and you're allowed to feel sad about having to resort to ending contact just to be able to function. The important thing is to remember why you ended contact in the first place. Don't let your guilt convince you otherwise. You've made a choice which was in your best intrest, so stick with it.
Other people are going to have feelings about what you do. They might judge you, be angry, be indignant. These things are none of your concern. They can believe that you're wrong, evil, selfish, ... Their opinion of you is their problem and their burden to carry, not yours. Distance yourself from people who can't keep their opinion to themselves, because this is not helpful. Set stern boundaries. Your decisions is yours. You don't owe anyone an explanation and it's not open for discussion. They don't have to understand, but they do have to accept it.
If you do decide to cut contact, the best thing would be to inform your mother of your decision, but don't engage in a conversation where she feels she can change your mind or tell you how wrong you are for doing this. Once you make the call, you're informing her. It's not a debate, this is not a democracy. Your life, your choices, your rules.
As someone who's gone NC with my father 5 years ago, I wish you a lot of strength, kindness to yourself, and a lot of love.