The whole flying thing that Becoming and others mentioned, makes the little bit of extra money for first class all the more worth it.
Seriously, it's not that much more, and even when it's booked solid, it's easy to scam yourself into an emergency exit aisle seat, lot's more leg room, and you usually end up by yourself.
The arm/leg/foot falling asleep thing is a circulation problem moreso than a "being a big dude" problem.........and forget about sleeping comfortably when you're big and on GH.
Oh yeah.....and wait until you have kids......the stares from other parents are comical at best.