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Two cruise lines that stand out to me using your criteria are Princess and Celebrity, and perhaps Holland America. Since it will be your first cruise, no matter which ship you choose it will dazzle you. These cruise lines are more reserved than some others, both in ship decor and how the cruise experience is presented. Celebrity's Solstice-class ships are like floating spas.
Now, if you want to really be bowled over you might want to consider one of the Oasis-class ships of Royal Caribbean. They cost more than cruises on other ships but these are both amazing ships that will let you do as much or as little as you want. I've been on both the Oasis and the Allure and am headed back to the Oasis next June. I
A lot of the cruise experience these days involves extra fees for certain things on the ship, and thus it is important to realize cruising on the major lines is not 'all-inclusive'. To do that you need to look at ultra-lux lines and that is often, but not always, out of reach of the average working person.