@HImom I use one of the smaller Day-Timer loose-leaf refills for pretty much everything. Their binders aren’t heavy-duty enough for my really enthusiastic use, though, so I found a place that sells really beefy aluminum ones in every size and configuration imaginable.
Getting back to your question, I don’t use heavy-duty paper, but I do have plastic or card stock dividers at pretty frequent intervals and have heavy plastic things at both the front and back.