I'd be tempted to go down the Atlantic coast and up the middle-ish of France (or vice versa). This assumes you're happy with the IOW-Cherbourg crossing, I guess - which is almost exactly the same distance over water as the shortest route to Ibiza.
Bordeaux - Leognan Soucats (LFCS) is a friendly place which has fuel, although not that cheap and you'll need cash.
On the other side of France, Verdun-Sommedieu (LFGW) is a great place for lunch at the on-field restaurant although possibly further East than you need.
Auxerre-Branches (LFLA) is a pleasant but typically sleepy French rural field, fairly close to the town.
French airfields seem much more likely than UK ones to have at least one hard runway, so a good nosey around the AIP plates on the
SIA website might be an enjoyable thing to do during early planning.
I have an immersion suit that I think would fit you, if you want to borrow it.
The 1:1,000,000 French 'Cartabossy' chart is a useful planning aid, if you've not come across it. Again, if you'd like you can have last years' for pre-trip headscratching.