There are multiple option. For once being in sheep form grants extra cold resistance, its also upgradable. There are a huge variety of clothes and accecories that reduce cold dmg. Blazing fire stone and undines water cloak are one of the best options. But wool coat, wool hat, winter coat and battle suit are very good options as well. There are even some decent option to buy in town. And the item varia field also temporary can reduce cold dmg. The options for reducing cold dmg are way more than reducing heat. It is absolutely possible to bring cold dmg down to 1 dmg.
And if all fails dmg boosting through with high hp is a possibility even if its not the intended option.
Thanks will fix that!
If you want a hint, the potion cant be found but must be made.
Hope this helps