Or, hear me out: take a cold shower for a minute, then turn it slightly warm. It will be painful. Repeat every day. Go outside with one less layer than normal, shiver for 5 minutes. Do this literally every day. Pretty soon, cold adaptation. The human body is nice like that, and your vascular system will thank you. Unless you have a really bad heart condition that wouldn’t allow cardio obviously because your heart rate will go up.