The Italian lakes have very limited public acces – no secluded beaches for the hoi-poloi!
The French Riviera is horribly (as in excessively and in the worst taste) built up.
I would choose, from second-hand accounts Corsica which can be fantastic, or Croatia.
of course West Cork would be ideal -especially as next summer is supposed to be a scorcher. There is a sailing school in West Cork with a small fleet of Wayfarers, that might be a good place to start.