1% milk works all the time for me. Just add in some butter and flour to make it a rich, creamy and thick sauce. If you have evaporated milk on hand, you might want to give that a try as it's creamier than regular milk.
If you have much, give of your wealth. If you have little, give of your heart. - Arab proverb
Because cream has enough fat to give the sauce a rich flavor and thick consistancy, you have to add a considerable amount of butter to compensate for the loss of fat when using skim milk. You aren't gaining a thing since you are just trading the fat and cholesterol in butter for what you don't have in skim milk.