As above wear what you like and ignore the comments.
But if you are serously intending to protect yourself against fire, don't play at it by wearing only the nomex coveralls.
You will need cotton or nomex underwear and socks and flying boots.
Your head & neck must be protected by a nomex hood, and a bonedome (or leather helmet and flame proof goggles if restricted room in the cabin)
Not much point in protecting your body if your hair is on fire and your eyes are steaming while the skin chars on your face.
In military flying I wore all that lot on every sortie.
In BOAC/BA we wear cotton shirts and polycotton trousers and make damnn sure that every eventuality (and a few others!) are taken account of on every trip.