the more you coddle your body the more it gets used to it and depends on your behaviour to keep the internal temp regulated as opposed to the body taking care of it itself. thats why older folks who go outside less and less also keep turning the thermostat up in winter. soon, the body can only operate in the narrow range of temp it has grown accustomed to.
believe it or not, cold showers. shower as cool as possible and then finish with all cold as long as you can stand it. when i first did this it would chase me out of the shower no different than if the water were battery acid. now the cold doesnt bother me except i dont like wearing clothes when the weather forces me to.