In the last few years, I've managed to cut the major stressors out of my life. The biggest one died last year. I've never had any success at masochistically pushing myself to the point of pain and misery. For me, pushing my limits and expanding the boundaries of what's possible has to happen in a way that feels natural--as if it's the next perfectly obvious step to take.
I don't see my body as something that has to be conquered, any more. I occasionally fast for longer than my normal IF period, but I never plan to. I'm simply not hungry, so rather than eat out of habit I wait until genuine hunger returns and then feed it what it wants. I don't decide how long the fast will last, either--my body gets the final word on that.
And expanding my cold tolerance is the same--if I'm truly uncomfortable and all I can focus on is how cold I am, I'm going to pull the sweater out of the bottom of my bag and put that sucker on.
I did spend years seeing my body as something that had to be beaten into shape. The results were inevitably dismal, demoralizing failures. Learning to listen to it, treat it as an ally, and have fun getting it to do new things has been far less stressful and more productive.