Here is the best result I got from a simple Google search: "Covid-19: International Travel" from France's Ministry of the Interior. It appears to be current. According to this, vaccinated travelers from the US (one of the "green" countries) do not need to test before entering France. You're considered "vaccinated" if you have had two Pfizer or Moderna shots at least 7 days before travel, or one Johnson & Johnson shot at least 28 days before, AND a booster (Pfizer or Moderna) no later than 9 months after your last shot (first of J&J or second of Pfizer or Moderna). It doesn't mention a second booster.
If you "can't get a consistent answer" to your question about testing, I suggest you consider the airline as the best source of information. They won't let you board for France without knowing that you meet France's entry requirements, because they don't want to have to fly you home if France doesn't let you in.
I got my second booster last week, preparing to fly to Europe in two weeks, not because it was required but because I think it will protect me from serious illness should I get infected, and to some extent from infection as well. I'm eligible based on age, and I'd advise anyone who is eligible to get the second booster. No one knows whether the current boosters "will... protect us against any new variants," because no one knows what variants might emerge in the near or far future. But my medical advice is worth exactly what you're paying for it. I hope you do what you can to protect yourselves and others before, during, and after your trip, and I hope it's safe and enjoyable.
EDIT -- As the previous poster noted, there are no rules requiring vaccination or testing for domestic air travel. (That's why I'll be wearing a mask on board.)