People often suggest that you put bedding in a coop when you move chicks there from a brooder so they can snuggle down and keep themselves warm. Until they start to roost chicks, whether with a broody hen or by themselves, sleep on the floor. Some adults, some silkies for example that can't fly come to mind, never roost but sleep on the floor. Some silkies do roost but some don't. Naked Necks (Turken) are considered a cold hardy breed. They have no feathers on their necks and about half the feathers on their bodies that regular chickens have.
I see no problems with your molting birds sleeping on the coop floor in those temperatures, though I'd want some bedding under them to insulate them. I see no problems with chickens that are molting roosting in those temps as long as they have good ventilation but no direct breeze blowing on them.
