Shame winter is over and the nights don't need it, but when I was looking for something to wear over winter someone suggested a coldroom outfit like the shelf packers wear in the frozen goods section of the super market.
I think this is far better. I'll be getting one for the next cold night. Figured others here might not know about them.
http://www.selkbagusa.com/Selk-bag-4G-Classic.aspx