The problem with day trips from Paris to Normandy invasion sites is that you spend so much time on buses between Paris and that part of Normandy, and then the sites themselves are widely scattered, so there's not much time actually seeing them as opposed to driving to them.
Overlord Tours has a tour designed for folks who can't manage one night up in Bayeux. You take the first train from Paris to Bayeux. The small-group tour meets right at the Bayeux train station. You get essentially a full day tour, then you are dropped off at the Bayeux train station to return to Paris. You are responsible for your train tickets, and it's a long day, but you get a much more comprehensive tour than the usual offerings from Paris.
Overlord Tour #2FS