The last time I visited Paris, I remember buying a Navigo Découverte card, but I bought only a zones 1-3 pass. This used to be on sale, but it appears it isn't anymore; it's been superseded by the « forfait toutes zones. »
Another thing I remember used to be sold is the « complement de parcours » — it allows you to travel outside the bounds of your pass on a per-trip basis, only paying for the portion outside the zones. But it appears there's no mention of this anywhere I look.
Do they still sell these “pass extension tickets?”
The Navigo Week pass now only comes with either all zone coverage (zones 1-5) or zone groups not including Zone 1 (such as zones 2-3, 3-4, 4-5). So the Navigo 1-3 zone week pass is no longer sold nor available.
The complement de parcours extension tickets are now apparently only available for monthly & yearly Navigo subscribers and only Monday to Friday; It's basically aimed at residents. Navigo has also changed so that on weekends, holidays and school holiday periods, Navigo passes that don't cover zone 1, get zone 1 coverage for free. A thing they're calling "dézonage". This again only applies to monthly and yearly Navigo subscribers, not to Navigo Day and Navigo Week passes.