I like to use drapes that reach from floor to ceiling, even over windows that are not full length. I believe the extra material helps to trap the cold air.
When it was time to purchase drapes for my bedroom, I noticed the width was the same on most of the sizes, only the length changed. As I was looking for drapes that were 84″ long, I decided to purchase a set with each drape wide enough to cover the entire window.
When I hung them, I used a curtain tie back one side and purchased a valance for each window. These drapes are energy-efficient, and when I sewed Velcro strips on each side of them, I was able to make them lock in the cold air at night. See “Dress Your Windows” at http://wp.me/pKNzn-t.
I not only did not buy two sets of drapes, I did not need two sets of tie-backs. I did the same thing when I purchased drapes for my office.