Need help planning trip after Paris!

How about someplace else in France? Normandy and Mt St Michel? Loire valley to see chateaus? Nice and the south coast?

BTW, I just spent 12 days in Switzerland, I never got tired of the natural splendor.

No need to go to another country, France has so much to offer. Normandy/Loire would be a great choice. With the fast train to Provence, you could also do that region plus the Riviera. You could also consider staying in Paris one more night. Your first day will be a jetlagged throwaway in all likelihood. All of this said, I don't think you would get bored with six nights in Switzerland either. The French Alps are also great, likewise Alsace and Burgundy. France is probably my favorite overall country to visit in Europe, and I've been to lots. Don't make the mistake that so many do of only seeing Paris. Not that Paris is not great, just that France is more than Paris alone.

Reminder we only have 6 nights

But you don't have 6 nights for other places, because you need to be back in Paris on the last night, for your flight home the next day.

I agree that you could easily spend the remaining 5 nights elsewhere in France. You could rent a car and see Giverny, Caen, Bayeaux, Mont St. Michel, and return to Paris via Rennes and Chartres.

Or, you could train to London or Amsterdam.

When are you traveling? My advice might change if this is a winter trip.

Italy: Cinque Terre OR Portofino or Venice (2 -3 nights) with Florence or Rome (3-4 nights) .

France: Loire Valley OR Provence (you will need/want a car) and visit Gordes, Lourmarin, Menerbes, Isle sur La Sorgue VRBO a cute little place near Gordes. Visit the Bastide de Gordes for cocktails on the terrace, or stay there if you wish to have a hotel.

U.K.: Fly to Edinburgh (two nights), train to London (4 nights) fly to get your connection out of Paris.

I agree with the others about staying in France. There is so much more to the country than Paris. If you really wanted to go to another country, Belgium is closer than Spain. Choice, choices.

What time of year? Either Amsterdam (3 hour train) or another part of France based on your interests. Provence, Burgundy or the Dordogne...depending on the time of year.