back when I was doing week+ trips to Paris and surrounds we would have a Carte Orange and get a week long pass for however many regions were needed. I've read here that this has since been replaced by Navigo Découverte.

Navigo

Suggest you check out the links in post #5 of forementioned thread.

If you're staying in the city (not heading out to CDG or ORY, for instance), then the cheaper plan (Zones 1 & 2 @ €16,80/wk) should suffice.

Definitely nicer than fussing with T tickets, especially if you sometimes put devices in your pockets (e.g. cell phones) that might magnetically erase them.