I agree with your concern over man made fibre shirts/pants etc (check out the inside label inside a BA uniform shirt or blouse, preferably the latter with a hostie in it!! think you'll find it says 60% If not only from the comfort point of view. I too wear nomex, I am very doubtful of the flame retardent qualities being retained after being put in the wash on a weekly basis anyway. Fire retardency comes from multi-layering, silk being best as an under garment! It's the heat that kills not the flames!
Other than that as already stated dress for the outside not the cabin, or at least have a grab bag with some warm kit in your instance.