Dining on Ile St. Louis (Paris)

Le Trumilou is good for traditional French food, with reasonable prices. It is just across Pont Louis Philippe from the island.
If you'd like to take away a seafood platter, Poget & Dewitt (on the island) has great oysters and other seafood - albeit on the pricey side. I think they have a few tables but it's not really a restaurant.

There are several place on Ile Saint-Louis you might want to check out.
There is a place named St. Regis. For breakfast, Coffee, croissant, and juice for very little money. Even had a small plate of cold cuts and wine one evening. On the same street is Café Med which is good for lunch. Still farther down the same street is L'Orangerie & Auberge de la Reine Blanche which is good for a semi fancy dinner. Reservations are a good idea. And don't miss the chocolate ice cream which is in the same block (other side of the street) from L'Orangerie. If you fool around with google maps, you might be able to use street view and "walk" to them before you ever leave home. Enjoy!

This isn’t on the island, but it’s an easy maybe 10-min walk. Atelier Maitre Albert is a lovely restaurant just across from Notre Dame, in the 5th. It opens at 6:30. It has a big, open fireplace they light on cooler evenings. All the meat entrees are spit-roasted and delicious. You could Google the menu and see if it suits you.

There is a place named St. Regis. For breakfast, Coffee, croissant, and juice for very little money. Even had a small plate of cold cuts and wine one evening

I love St Regis. Mostly because of a wasted sunny afternoon cafe sitting there. Sunny afternoon & interesting crowd. Several models were doing photo shoots by the bridge in front of us. One model sat down next to us in a bright blue feather coat. I think her partner was live streaming something. (it was fashion week) Waiter was very friendly and happy to keep pouring drinks. Just a wonderful afternoon

in addition to Berthillon for gelato there is an Amorino on the island

Les Fous de l'Ile on Rue des Deux Ponts on the north end. Chicken is their specialty, which you will observe as soon as you walk in.

Café Med, which TC mentioned, is good for dinner as well as lunch. We love it. Incredibly low prices (like €14 for 3 courses), great décor and ambiance, and the food is good. My favorite 3 course meal there is: puréed vegetable soup, curried chicken with rice, and tarte tatin… : )

My favorite café in all of Paris is La Flore en l’Ile by the pedestrian bridge. Sitting outside is wonderful.

I’ve stayed on Ile St Louis many times, sometimes for a month, and there aren’t that many places to eat (maybe 12). You just walk the main street (rue St Louis en l’Ile) and the one cross street, read menus, and pick one.

I guess I am seconding suggestions LOL. I was going to also suggest Auberge de la Reine Blanche. I have dined there without a reservation but I usually eat fairly early. It's very small so if going later in the evening perhaps a reservation is the way to go.. And of course, the Insta-famous St. Regis - love it for breakfast or a cocktail later. I've also enjoyed Atelier Maitre Albert across the river. Not sure if it is chilly enough in May for that marvelous fireplace? :-) I've also quite enjoyed La Flore en l’Ile. About a 15 minute walk (from Berthilion) into the Marais I would also suggest L'Amuse Gueule -- I'm still dreaming about a seafood quiche I had there as well as my hubby's risotto https://www.lamusegueule-rambuteau.com/

If you love good Italian style coffee (French coffee is fairly terrible) then the cafe Cafeoteque is just across the river near Pont Marie on Rue Hotel de Ville. Excellent coffee, some outdoor seating, and the usual cakes and such. We make it point to stop there several times on each trip when we are in the area.

I like the coffee at La Flore en l’Ile café.

If you love good Italian style coffee (French coffee is fairly terrible) then the cafe Cafeoteque is just across the river near Pont Marie on Rue Hotel de Ville. Excellent coffee, some outdoor seating, and the usual cakes and such. We make it point to stop there several times on each trip when we are in the area.

I used to agree... but when did you go last? My last two visits in 2022-2023 were disappointing. Unfriendly, borderline hostile service, and good coffee is now available in many places in Paris so the drinks do not "shine" as much as they used to.