Versailles is indeed a whole day out!
I don't know about dinner on board the boats, but I think the Vedettes du Pont Neuf (based by the Pont Neuf, funnily enough 😆) are smaller, nicer and more central. It's a great way to take the weight off your feet and see all the sights for a couple of hours.
Otherwise, I recommend exploring the Ile de Cite, preferably arriving at Cite metro with its Hector Guimard entrance where you emerge right next to the flower market, having a look at how the reconstruction of Notre Dame is going (very slowly, inevitably!), paying to visit the Sainte Chapelle, popping over to the Ile St Louis for an ice cream at Berthillon, and from there you can easily walk to Les Halles (for the Pompidou centre), which has lots of good restaurants, or the Marais with beautiful 17C buildings and trendy shops and restaurants....
....OR you could head over to the Left Bank to check out the Latin Quarter, Shakespeare and Co (very crowded nowadays, not like when I stayed there 30 years ago!), St Severin Church etc.
I also recommend a big loop on the left bank, taking in the Jardin des Plantes, the Grand Mosque, the Pantheon and Rue Mouffetard especially Place du Contrescarpe, the quintessential pretty Parisian square.
Also, Montmartre- Abbesses is Paris's deepest metro stop and has another beautiful Guimard entrance. Take the funicular up the butte (costs the same as a metro ticket) and check out Sacre Coeur and the view- including the Eiffel Tower. After dusk it goes all sparkly every hour on the hour.
Don't actually go to the bloody Eiffel Tower. You'll probably ignore me though 😆
I know nothing about good restaurants, being a skint vegetarian!