Clothing and warmth are vital for citizen survival, especially in winter. Firewood (Woodcutter) is consumed by houses to keep citizens warm. A shortage leads to freezing and illness. Leather Coats (Tailor, requires Leather from Hunters), Wool Coats (Tailor, requires Wool from Sheep), and Hide Coats (Tailor, requires Hides from Hunters) are worn by citizens to protect against cold.
Ensure a robust firewood production chain. For clothing, establish a Tailor once you have a steady supply of leather or wool. Wool Coats are generally the most efficient to produce if you have a Pasture with Sheep. Citizens will automatically equip the best available clothing. A lack of clothing leads to lower happiness and increased susceptibility to illness.