Haven't seen these things yet, so will put it them as suggestions.
The Bateau Mouche, or tour boats to see Paris from a tour boat on the river Seine, is well worth doing. In addition to being a thankful relief from tired feet and walking constantly, it gives you the option of seeing Paris from a totally different perspective, from the river, and there is also the tour guides history of the monuments and bridges you go past. The one I took had a history of each bridge we went under, which was fascinating.
A few other places in Paris that I would happily return to, are Place de la Victoire, just north of rue de Rivoli, not far off the beaten track, but perhaps less frequented by tourists.
Place des Vosges, in the Marais. Simply fabulous.
Eglise Saint Severin, on rue Saint Severin, in the Latin quarter. Spectacular pillars in the form of tree trunks.
Museum of Cluny - among other items, the unicorn tapestries.
Museum Carnavalet, unofficially known as the museum of the history of Paris.
Enjoy your trip!