Sheep would be a great resource mechanic for winter weather resistance, making spinners (a wood crafting building, or additional item created in the furniture building like the blacksmith makes different items that all require steel, that would use wood/wood planks but not require heavy tools to craft) as an early luxury item for wool that gets collected every spring the same way milk is for cows and then wool blankets as additional luxury item that provides cold weather resistance like firewood does.
Since sheep might not offer as much meat as cows but provide wool they could use less villager food too, and require a lower level of fertility for their grazing area to sustain them since they would only output meat and wool instead of the high levels of meat plus milk/cheese that cows do.
TLDR;
Cows = high meat + milk/cheese BUT needs lots of herders and grains/root veggies + decent grazing area
Sheep = low meat + wool for winter (introduces new item resource/luxury goods mechanic of Spinner/Blankets) BUT needs less villager resources (herders/food) + can survive on less fertile grazing area
