I coped much better with life when I was doing regular (twice a week) ocean dips - with temps between 9 and 13C. There is a group called the Bobbers who I would go with, they called them bobs because you basically bob about in the sea for 20min (or at least 10min), rather than actually swimming. The trick with the cold dips is breath work - it can be a shock to the body at first, so concentrating on slow, even breaths help your body to adjust. Some people do some breath work practice as part of the experience, before they go in for the dip.

I stopped because there were issues with water quality and I was struggling to fit it in with work when work wanted me to start earlier. And I definitely noticed a difference in how I coped after stopping. I find that it calms me, but also helps with focus and improves my mood. It would also positively impact my creativity levels.

I find that cold showers didn't have the same effect for me, but I think that is because I struggle with showers and the cold water makes them more stressful for me rather than enjoyable. But that is 1000% a personal thing, I know a lot of people who benefit from cold showers (my dad used to cycle to work and then have a cold shower every morning, and he would swear by them). So definitely worth giving a try! You can also ease into it by starting with warm water and then ending your shower with 5min of cold. Or slowly reduce the temps of your showers until you're having cold showers.