I can't think of a situation where you would use one word but not the other.

They're exactly the same. I think 'somebody'is a bit more common, but it's personal preference which one you use.

As far as I know, there's no difference between "someone" and "somebody."

You can safely ignore all of those opinions. Some people try to make things more complicated than they really are. Other people like to give an opinion just for the sake of saying something. You can use either of these words in any situation. The same applies to everybody, nobody, anybody. The 'one' versions are just alternatives.