I have booked at Hotel Massena for April 1st. It is located near Massena square which is a block or two from the old town. Rates in summer are 160 or 200 euros. Rick Steeves recomends it.
I will include it in my Silversea cruise report either during or right after our return.
We stayed at the Negresco 40 years ago. It was 'snooty' then and still is.