You seem to misunderstand body temperature.
See
Thermoregulation - Wikipedia, the free encyclopedia
The point of clothes is not to warm you up, but to keep you warm, meaning you have to use less energy yourself to do so. Wearing clothes does not change your internal body temperature.
Clothes work by trapping air close to your body, this air then warms up to your external body temperature. Therefore any cold outside your clothes has to cool down the clothes and cool down the warm air before it can cool you down, clothes add a buffer to coldness.