Humans are not the same shape as comic and video game characters. For example, Granny Rags has skinny limbs. And a shirt. And a jacket.
The more layers you have, the more bulk you’ll have.
So… don’t have layers:
Here there is no shirt under the jacket. It ends far enough down to tuck it away securely, but won’t fold or add additional bulk to my costume.
This also works for vests. You don’t want to make a whole vest? Just make the front and attach it to the inside of your jacket :D
See more about this costume: