These are not needed spoilers because they are more coding related than story related.
Frostbite is something that can occur when you are in someplace cold. So because the village is in a cold place I use the variable to track how cold the MC is. So the colder you are the slower you can react which is why it lowers your stat (during the check only).
Phy_boost is the stat that refers to how warm they are (either by wearing a warmer coat that your partner brings, or a special suit that Anthony gives you. Or some powder you can consume from Catherine which has a decent phy_boost increase but also adds +1 to Frostbite as the powder only makes you not feel the cold the negative effects aren’t stopped)
Basically what your physical stat is for every frostbite you incur it will be reduced by that.
For example Tristan has a physical stat of 50 and incurs 5 frostbite during checks his physical stat I’d reduced to 45. Then let’s say he had anthony as his partner which gives him that insulated suit (phy_boost 5) that then bumps the physical stat back to 50 so negates the frostbite.
you don’t HAVE to not search the village the higher your physical stat and your phy_boost is means you can search for longer. The humanity >49 isn’t required it just helps at that point in the search.