Basically I want to create a world in which some of the humans have developed a higher body temperature in order to survive cold, harsh climates, such as the poles or even tall mountains. The reason behind it is rather selfish: I just want them to be a sort of barbarian like nation wearing skimpy outfits, something along the lines of Tarzan (please do not dwell on this aesthetic aspect though, just the scientific implications).
I know that the human body goes into heat stroke at temperatures of over 40 degrees Celsius/107 degrees Fahrenheit, but I was wondering if there's any way for it to evolve to overcome that. How would that affect a human being's appearance? Would they need a better vascularized skin, maybe a larger heart? Would this have any impact on their height or muscular development? I was thinking about the fact that an increased pilosity could help them maintain body heat better, but the idea of ape-looking humans does not appeal to me. Perhaps they could have a thicker skin instead? Also, I want my evolved humans to be mostly hunters, so quite active, therefore I need to know whether this increase in body temperature would have any impact on their diet as well.
I remember reading that monks in Tibet can increase the temperature in their extremities (such as hands and feet) by up to a third in order to prevent frostbite, but the explanation for that was meditation. Obviously my frost barbarians won't have time to meditate, so I was thinking of a more permanent solution.