Plenty of good advice up there, but just in case it's useful...
RAF suits come in 9 sizes, numbered 1-9
1-3 are for shortarses, 1 is thin shortarses, 3 is fat shortarses
7-9 are for tall blighters, 7 is for a beanpole, 9 for a tall fat blighter.
There are two flavours of RAF suit, the fast-jet suit has no thigh pockets making it more comfortable but less useful in a light aircraft, the truck / helicopter suit has thigh pockets you can put your checks, map, etc in for visibility in flight.
I also prefer RAF suits, but ex-Luftwaffe suits (in grey) aren't bad and are usually available cheaply second hand from the normal places, you just have to unpick the thread to remove the little German flags on the shoulders.
G