You don't need their permission in order to have a (better) life or quality of life.

Also, being a mother does not mean that you are not entitled to find any happiness in life nor that you have to live the rest of your life being at their disposal. This is not selfish, this is healthy. They are adults and at some point, they need to fly with their own wings.

I would tell them your decision and let them feel whatever they feel, that is fine. What is not fine is to let how they feel influence what your heart wants to do. Again, they are adults. You do not have to justify yourself to them. Make your plans and do what *you* feel.