In minus 35 degrees, the modern alternative to fur is down filled, water resistant, breathable synthetics. It’s production is not environmentally friendly and it won’t keep you nor as warm or as dry + down-plucking too, is controversial. But that’s sometimes what’s available to purchase, so there’s not always that much choice.
Synthetic fleece is another warm option, but the current process used to turn plastics into the warmer types of fleece is in fact directly environmentally bad - I personally stay well away.
Boiled wool clothing is better but not warm enough in less than ca minus 15 degrees and not commonly available nowadays + yes, it requires sheep (though they need a trim anyways, so not a bad option).
I guess, what I’m saying is that fur has its place (the real cold) and far from all types are farmed for fur alone.
Humbly,
Hermit