That's probably the easiest, it's already made, and probably not too expensive. I used black Dickies coveralls for a tie fighter pilot I did last year.
I made all that stuff (except the helmet) before I realized you could buy it. My Jango is being done right. If your picky there are a couple of board members that make realy nice suits to your size specifications, but it'll cost more.
Your best bet for coveralls is to get a pair of Red Kapp coveralls (can't think of the specific color right now) and convert them because they make the closest in coloring to the color you want for a Jango flightsuit out of all the major coverall makers. Look for Skalen Fehl's (sp?) thread of his suit and you can see the kick butt job he did on converting a pair.
I have a pair and they would have been perfect if I hadn't made my own.
Now if your thinking about going with two pieces, a separate top and bottom...then I'd always thought about looking into those hospital garbs (don't know what they call them) because they come in a wide range of colors and look comfortable to wear. But I don't know if they make them with long sleeves or without the V neck? But I'd think it'd be easy to alter a top of one of those to have a double sleeve.
How are the Navy blue coveralls weathered and recolored to look more of that lighter more accurate purpleish color? Im in the military and we wear dark blue coveralls so I have tons of them hanging in my closet. But I need to know what to do to conver them to the right color.