Instead of completely neutralizing body temperature, the Thermal Tuning enchantment should just slow down the rate at which body temperature changes, but ONLY when it's moving towards an extreme value (So that trying to cool yourself down in a hot biome doesn't take longer for example).

Just wanted to add a +1 to this suggestion, liekwise findin the full neutralizing of temperature when using 1 armour piece with Thermal Tuning a tad powerful.

Could it be graded similar to leaf and Wool, so that only a full suit of armour with all pieces with Thermal Tuning enchantment then move towards full negating or the larger pieces providing more weighting ie chest plate, legs, helmet and finally boots adding slightly different weightings of effectivness to negate temperature effects?

really like the mod it adds a really nice element to minecraft to have to worry about etting to hot or cold