If you go with off the shelf FR coveralls, they actually can get a lot of customization so you can do it with one piece what we do with two pieces well enough; we just suck at sizing clothes (despite having every single person's measurements on file). I'm tall and gangly and was able to find a pair of comfortable coveralls no problem, and I think they went by a combination of inseam, size, and a tall option, with a cinch around the waist. Between coveralls and boots with zippers it's way faster to jump into than the old setup, no question.
The 'two layers' of the new NCD jacket is BS though, and no way the new one performs as well as the old setup (tshirt, blue shirt, black jacket) in a flash exposure. The baggy air pockets and actual layers between the different items provided a huge amount of protection, so it was really just your face and hands that were exposed. Still waiting to see what the actual tests showed, but not sure if any was done to compare them against the old NCDs.