It sounds like you're describing the
Circa system offered by Levenger. Pages can be inserted and removed easily, and pocket folders are available for loose documents.
Others offer the system as well. I think the system is produced by a company called
Rollabind and simply rebranded by Levenger, so the two are cross-compatable, and the Rollabind stuff is often cheaper. I believe that Calirfontaine makes a
similar product too. It is offered in A4 format.
You can search FPN for reviews of all of these systems; they seem to elicit strong opinions from most of us. Among their supporters, the popular thing to do is order a paper punch (about $60) and some rings, and then use our own preferred brands of paper.
Good luck!