I could argue with you over whether it's easier for a fat guy to conceal or a skinny guy, but I won't...
What I will tell you is what I tell any new carrier -- don't over-think it. Surely, you need a good belt and holster, and surely you need to give some thought to wardrobe -- if you like to wear tight, untucked T-shirts, for instance, you may want to go a size larger. But the fact of the matter is, if you mind the basics no one will spot your gun.
In reality, no one -- in most cases, not even a policeman -- is looking for a gun. It is normal for a new carrier to be a bit paranoid about it. After all, to you it feels like all of a sudden you are wrestling with a nekkid fat lady in public; but it's that nervousness that will give you away if anything does, and not the gun itself.
Resist the urge to constantly check yourself out in shop windows, or do a check to be sure the gun is still in place, or put a hand on it to readjust the position. These sorts of things are the tells that can give you away.
Just put your good, secure holster on your good belt, make sure they are positioned comfortably on your body, secure your gun properly in the holster, and go about your business in your normal fashion.