We recently built on a downstairs bedroom, so now we can shut off the upstairs. Since it is an open staircase, I took 3 thermal backed curtains and hung them on a rod on the banister side & where the stairs start. I just put the 1 panel at the stair bottom yesterday, so I am anxious to see what the temp is upstairs today.
If you look at old movies, you can see where they had curtains all around the 4 poster beds.