French law does not forbig nudity as such, only "exhibitionism" - but then, who decides which is whih? Naturist organizations have been trying to have the law made clearer on that point to exclude genuine naturists, but so far to no avail.
On the whole, be careful: it only takes one person to be offended to get in trouble with the police (especially if you are a lone male). Most cases involving genuine naturists end quickly with the policeman telling them to be more careful. Very rarely such cases have been taken to court, but there have been no convictions for years.
Also take into account the fact that Normandy is not Provence or Aquitaine, in other words it is not "beach holiday" country - so that many people that you will meet on the beach will be locals relaxing close to home, not holidaymakers, and may be less tolerant than holidaymakers further South.
Still, thousands of people change daily on the beach without a towel every day. Just be careful not to explictly draw attention to yourself.

There is a nudist beach at Merville-Francville which is on the far side of the Orne estuary, across from the ferry port. It's a couple of miles over Pegasus Bridge, been there a few times as we are regular visitors to the area. Large section of the beach and dunes included.