I don't think you will find a French camp site where cozzies are allowed in the pool but you might try Euronat, CHM Montalivet or Chateau Guiton in the Bordeaux area.
Euronat would be the most accommodating but it is also the most expensive but has plentiful children's activities in season.
Chateau Guiton is small but very comfortable with a slightly hippy atmosphere and no restaurant but splendid "repas communal" on one or more evenings each week. Also I have used a swimming costume in the pool there.
CHM is similar to Euronat but less "suburban" in its feel.
I have not been to Guiton or CHM for several years but by all accounts they are still as I have described them.

Our first experience of naturist beaches was in 1978 and 1979 and we haven't looked back since! It started a trend of naturist beach holidays which continues to this day. Those beaches were in the Landes area south of Bordeaux (Arcachon to Mimizan). They are huge, long and wide beaches backed by magnificent sand dunes. A quick check at https://en.plages.tv/naturist/l-aquitaine shows they are still naturist. The only warning is that you have to be careful about swimming because the coast is on the Atlantic and it has strong currents.

As an addendum to Sunandbare's reply I might add that staying at a coastal site like Euronat or CHM will mean that there are lifeguards on the beach by the site and they will have designated a swimming area without tidal rips which are very common on that coast and are are far more frequent cause of drowning than the rough seas you can encounter.
I might also add that the beaches in front of all the Atlantic naturist camps are totally open to the public with no restrictions.

You might consider renting a Gite in that area, many years ago we found a lovely little house near Begadan which is about a 20 minute drive from the beaches of Montalivet, the garden of that gite was small and shady after about 3 pm but it was very private so we were able to sunbathe naked most mornings.

We recommend Euronat.

If your wife is not likely to be nude at a nudist resort perhaps she’d feel less pressure and be more relaxed at a textile campsite that’s close to a nudist beach.

We’ve never been to the area but there must be something like that around there.

A decent compromise maybe.

I forgot to add something which I have posted several times elsewhere which is that there are always so many people coming and going at Euronat that our wife will not feel conspicuous if she remains fully dressed.
Although swimsuits are definitely frowned on allowance is made for menstruation so that on hot days a "cover-up" shirt worn with or without  bikini briefs is OK. In fact, my wife often wears such a long shirt with sleeves to protect herself from the sun.
Also before breakfast and in the evening most people are fully dressed.
The same is true of all the French naturist sites.