I have 3 silkies in my mixed flock of layers.
It's not as cold here as many places but it's been getting into the teens at night. I built my coop for hot weather, not cold. Ceilings are high and ventilated. The walls are not insulated.
Everyone is just fine. I admit too that I worry about about my most broody silkie. She absolutely refuses to get off the nest and doesn't move except to adjust the eggs or pull them back under her. I have another half-hearted silky broody who usually spends nights in the nest beside her (especially if she can steal an egg or two) and often the young sex-link pullet she hatched for me a few months ago piles in as well, so I think they are cosy at night.
But yes, I find silkies to be as hardy and adventuresome as any of my standard layers. In fact they are often braver (or more foolhardy, can't decide which!) but they are outstanding. Maybe I just got lucky, but my girls lay almost as well as my standard layers, when they aren't broody. Their eggs may be smaller, but the yolks are just about as large as the bigger eggs. All in all I'm very pleased with them and experimenting with adding their genetics in with my laying flock. In fact my broody is setting on a clutch of all silkie eggs this go-round (RIR is the daddy).