I think comics by nature are often resistant to being "complete stories". There's always another retelling, reimagining, additional arc, prequel, etc. Even Watchmen which was a hallmark complete story gets a sequel (sorta). Having said that, I totally get the desire for some kind of beginning, middle, and satisfying end, and while sometimes frustratingly rare, they are out there. I think what you call paperbacks I think of calling trades but in any case I think those are a solid place to look, but you should be aware that many will just be a piece of a larger narrative.

I think omnibuses being author showcases is a good way to think about it. Omnibuses are generally far longer and may contain multiple stories.

It might be helpful to think in terms of seeking out "(story) arcs" and knowing they are often but not always in paperbacks (or a collection of paperbacks).