What girls are these? Remember some breeds are more winter hardy.
I would make sure they have a full crop at bedtime. I realize folks like to feed whatever they choose but greens and non grains will not keep them warm. Save your scratch grains for the evening time. I make sure they have feed on demand. The winter time is not the time to skimp on feeding IMO.
Add more bedding to the floor if you think they need it.
I try to keep a full coop of chickens. This is why I wonder why folks downsize in the winter. Seems to me that's the time to upsize. The more bodies the more heat. Too, since they let up laying if you want eggs in the winter, I think it's the time to keep and access of hens.
I would stand in your coop, wet your finger and hold it up. See if there are any drafts. Ventilation is best up above to it draws the moist warm air that rises out of the coop.
I don't ferment feed, but I do buy the Agway Egg Producer Pellets that are 21% protein.
Of course there may be different opinions on the matter and you have to decide what's right for you. There's more than one way to skin a cat , you know.