While I was married, we both slept naked, now that I am a widow, I have reverted to nightwear of a long t-shirt,as apparantly you can no longer buy jersey cotton nighties and flannal is a thing of the past too.
From now until May, the heating is on, although I am still sleeping with a summer quilt - my winter eiderdown keeps asking when it is coming out of the blanket chest, though.
In cold weather I warm my bed with an electric blanket, which I pull out before going to bed, as it is lumpy to sleep on, and usually add a lightweight quilt and two cats to the keeping warm equipment.
At no time is the window open at night unless the temperature rises above 40 degrees centigrade, which is unlikely at night.