Can you please confirm, if arriving on a Sunday (day 1 of 7 days > leaving the following Sunday), would the best combination of passes be: Sunday (day 1): a Navigo Day pass and a Navigo Découverte week pass (for days 2-7)? The above question is based on travel only in Zones 1-2 and one trip to Versailles. The above also assumes that there is no difference for one day between a Navigo Day pass and a Ticket Mobilis.
For a Sunday to Sunday itinerary, yes, a Navigo Decouverte with a one-day pass for Sunday and week pass for Monday to Sunday is the best pass/fare combination for Paris.
This assumes you will make 4+ trips on the first Sunday to make the Navigo day pass worthwhile. The price of Ticket Mobilis and Navigo Day Pass are the same (when the zone coverage is the same).