In the winter of 2016 I replaced my morning exercise with the Wim Hof Method, a combination of breathing exercises, meditation and cold showers.
Very quickly my response to cold felt like an energising electric charge. By the end of winter I was regulating my temperature in an ice bath.
The technique has been backed by science and becoming increasingly prominent with peak performance athletes and people with auto-immune conditions. I find it really useful during low periods, helping with focus and energy. Highly recommend it.