Wool is excellent so worth considering. However, although I used to own a pair of military surplus winter wool pants and loved them, unless they are built right, your leg movement while biking might be restricted (I didn't bike in them, just walked). It'd be best to see how much movement they provide you before you purchase them. Also, keep in mind, especially if you currently don't commute in pants, that the pant leg needs to be tied up in some way to prevent it from being caught in the chain.

At this time of year, the snow may be wet so a water-resistant shell, especially on your upper body, might be sufficient: the water-resistance would also provide wind resistance and thereby reduce convective cooling from cool wind going across your body as you bike, this is the first change of clothing I make when moving from summer to fall.