Fleece bottom sheet, no top sheet, duvet with flannel cover.
This time of year - flannel sheets, feather duvet, heavy wool blanket and velux blanket on top of everything because the dogs sleep on the bed and it’s easy to wash. At night dogs snuggle in and help keep me warm. I get cold at night and like lots of covers.
Me too! But of utmost importance is Heavy Feets. Unless it’s summer, I need to have a small stack of folded blankets (and my robe, and maybe other stuff) at the foot of the bed so my feet are really noticeably weighed down. It sounds dumb, but it’s almost like I need that to feel “safe” enough to fall asleep. I’m not sure why, but I just can’t relax enough if I don’t have Heavy Feets.
(My husband is the exact opposite and can’t stand stuff at the foot of the bed. My side is literally a foot higher than his at the foot! :D)
Oh, and I always need to have my shoulder (I’m a side sleeper) covered, for similar reasons. Even in the summer as a kid living with no a/c, I’d pull the bed sheet up behind my body just so I could have a tiny “cape” of sheet coming over just my shoulder/upper arm.
At most, a light sheet, usually not even that much.
My partner, on the other hand, needs blankets, comforters, gloves, socks, a knit cap, etc.
On top of the sheets, under a down-feather blanket. I also usually have a fan going, except in the winter time.
I dress for the weather, even when sleeping on my floor mat. Nothing on me in the heat of summer, two or three covers and a sweat suit in the cold of winter, and everything in between.
I have a summer duvet and a winter duvet. When it’s really cold I have a heated matress pad. Of course, I share a bedroom with Nanook of the North; we keep it cool year-round so he can sleep. It’s easier to pack me in than to cool him down.
Ideally, I’d have the room very cold and have several blankets and nothing less than two comforters, just as I did when I slept in the 4th bedroom pending my separation and as I did when I was single afterwards.
Never slept so well in my life. Probably 50 lbs worth of blankets. Solved my restless turning and leg movements.
Even though there’s no ‘varies’ option, I chose what I’d prefer to do year-round, which is a sheet and a snuggly blanket. Mr. Tao and I sleep in the same bed, but have individual blankets, because otherwise one or the other of us would just take it all. Plus, the differences, in that he likes stiffer comforters, I like snuggly blankets.
That said, I keep the ac on nice and cool so I can wear my blankets as often as possible, and Mr. Tao loves to rib me about putting the ac on just so I can snuggle deep in the blankets. 
We don’t run the heater in the winter very often (we’re in California, so our version of ‘cold’ probably has most people who have real weather chuckling), and almost never at night. We like the house cold, but one of my greatest small pleasures is mummying up under nice warm heavy covers. Right now we have a sheet, a quilt that the spouse’s grandma made, and a down comforter. Waking up in the middle of the night cold because I’ve thrown the covers off, then burrowing under them and getting warm again is wonderful!
Oh, and we also have several little furry space heaters (most people call them cats) who love to sleep with us. Half the time I wake up feeling like Gulliver pinned down by the Lilliputians, because they spread themselves out on either side of me and weight the covers down. Except for Ozzy, who likes to sleep on the spouse’s face (or as near to it as he can manage without getting punted out of bed.)
Another vote for keeping the house just above arctic at night and piling on - or off - the blankets as needed. The colder the house at night, the less likely I am to suffer the agony of night sweats. I always sleep better in colder temps anyway.
With the addition of Miss Widget to the SuperKitty contingent at Casa Scubaqueen, I now have my own personal hot water bottle with fur. At 13 weeks, she’s just big enough now to snuggle - and her body temp is somewhere about 200 degrees F. And the place she likes to snuggle is on me - by literally draping herself across my ***neck ***(I’m a side-sleeper).
Between her, a sheet, summer blanket, bedspread, and a light thermal blanket over that, staying warm is no problem at all.