I "needed" a little bit more granularity with the cold and personal warmth rules while still keeping with the general feeling of the base system because I run in a world with a little bit more of a earth-normal and varied climate world. Note that the numbers for the new stuff are not final as I don't have a super strong grasp of the economy of the game at the moment.
I have 6 main levels of temperature: Freezing, Cold, Cool, Warm, Hot, and Sweltering. Cool and Warm don't require rolls and they're hold overs from the weather generation system I use. Cold requires a roll every Quarter Day and Freezing requires a roll every hour (or turn). I do an inverse of the Cold condition for heat, but that's not important at the moment.
I've added a new trait to some armors (and a Winter Clothes gear) added a few armors.
Armors are: Leather Jerkin (AR 2, 3sp, Light), Leather Hauberk (AR 3, 5sp, Warm), Chain Shirt (AR 4, 18sp, AR 2 vs arrows/stabs), Chain Hauberk (AR 6, 24sp, Heavy, Warm, AR 3 vs arrows/stabs), Breastplate (AR 7, 65sp, Heavy, modifies MOVE by -1), Plate armor (AR 9, 80sp, Heavy, Warm, Modifies MOVE by -2).
Additionally, a Closed Helmet and Great Helm has the Warm trait if you don't already have the Warm trait (to prevent people from running around in cold weather with just a helmet and claiming warmth).
The Warm trait simply treats the temperature as if it were one category higher while performing any activity during a Quarter Day other than RESTING or SLEEPING.
Winter Clothes (crafting info as Great Fur, but requires 1 pelt, 1 wool) give the Warm trait as well, and can be worn under armor that doesn't give the Warm trait.
The Great Fur (which I'm interpreting as a furred cloak), Blanket, and Sleeping Fur still work as normal (giving a bonus to the resistance roll). Additionally, like a blanket, the cloak also gives a +1 bonus to resist the effects of Cold.