DO NOT GET A NOMEX FLIGHT SUIT!! Mel, no offense but I was in the Navy and wore flight suits constantly. The chemical coating that makes the flight suits fire retardant does not allow the fabric to breathe at all. They are hot in the summer and cold in the winter.
I did make a ghillie suit out of an old flight suit because of the one piece design and I knew all the jute, burlap, and vegetation would nullify any temperature properties but other than that, flight suits are not the best thing to wear. They are thin and tear easily.
If you are looking for a one piece design, the better choice is to get a set of Dickies overalls. They are cheap, 100% cotton, and come in brown, khaki, OD, and black.
Just my $.02 but I think you'll make a mistake with a Nomex flight suit.