We used to do the Portsmouth to Cherbourg route on the catamaran in 3 hours in the Summer and head for Brittany.
We stayed at my sister's place which was SE of Quimper.
Brittany is great if you love anything apple-y: Apple pies, Tarte tatins, ciders etc...
Then you could go Lorient, Nantes, Bordeaux.
Or, if you go across the channel, Le Mans, Tours, Poitiers.
All depends on your budget and how much time you have.