I have the opposite problem--in the summer the air conditioning hits the bottom floor first and works it's way up--if I turn it down the upper floors get no air and in the winter same problem--upper floors get no heat
I had a space heater down there but ended up having nightmares about all my fabric catching fire (kept going back downstairs to 2-3 times to double check that I had turned the heater off). I felt like I had OCD so I opted to move back upstairs when my daughter and her kids moved out. I hope you get a good answer!