Everything stretches, but in this case not 1 size. I even sized up. So or get your usual size or even size up. To be safe get your own size M.
If you get S while you're M, it will look like women jacket on you. It will be too short. It will in no way stretch in the lenght, because that's just not possible... like jeans do not stretch in the lenght, but only at waist and thigh where there is pressure.