Most provide measurements. Then you can go measure across your bed to see where it would fall.
I don't buy quilts anymore because I decided I prefer a bedspread that goes all the way to the floor around 3 sides. I tried the whole bedskirt thing for years and I just hated them. I also don't like having that area around the bed showing, so bedspreads work for me.
Like you, I also like 100% cotton. All my bedding, from the sheets to blankets to bedspread, is cotton.
But I'd say to just measure and get a feel for where it would fall. I would think that a King size would be good on a Queen bed because you'd just have that much more side and bottom end coverage.