I can't imagine living my life with hypersensitivity. The way you describe hearing your neighbor's mechanical keyboard typing gives me chills. There is this thing I heard about before it's called the sensory deprivation tank. It's isolation tank filled with salt water that is your body temperature and you will float in there silently in the dark. I don't know if that is for you but it could be very therapeutic although you did describe how it is to hear your own internal sounds as well so I truly do not know if it could help or not.