Most people nowadays associate skiis with skiing down a mountain for sport or leisure, however, the historical cross-country origins of the ski were much more practical than that. Skiing was a revolutionary technology that enabled Eurasian peoples to cross vast distances in the taiga/tundra biomes and the spread of the technology facilitated the spread and conquest of many peoples and languages. A hunter or a warrior on skis was several times faster than a large prey animal or human opponent in ankle-deep or deeper snow. It was the wheel or chariot to the northern peoples. Modern militaries still use the skis and they saw extensive use in WW2 wherever snow was present on the battlefield or behind the lines.
The earliest skis had a longer ski on the non-dominant foot for sliding and a shorter ski on the dominant foot for traction, while more modern (1800s) designs were symmetrical, the underside of both skis being coated with both fur or wax for friction and glide, respectively. Implementing skis in VS seems extremely straightforward to me and would provide a fun + historical way to move around in snow in the winter.
Winter transport can be improved in other realistic ways as well. I can only speak for nothern Eurasia - winter there was arguably the best season for transporting bulk goods (lumber, ore etc) on sleds. Lakes, rivers and marshes are all frozen solid and provide a free, flat, clear highway for goods to be moved around.
Cargo was driven by oxen or horses and smaller passenger sleds by dogs. Individual hunters/travelers would often prefer to drag their baggage or their kids on a small sled instead of carrying the weight on every step. A sled is significantly easier to build, maintain and repair than a cart with wheels and axles, and only later in the medieval period did they begin to be reinforced with iron blades and fittings.
Autumn/spring represented the break in traveling, with the ground getting wet and soft and ice being unreliable but still enough to prevent boats and ships.