Great Danes
Yes, the largest breeds of dogs available are gentle giants and one of the most laid-back breeds. They do not need as much exercise as other breeds of their size, and as long as they get a good walk in every day and you have their environment enriched at home, you will have one couch potato on your hands.
Like all other dogs, they can get goofy and playful, so you will have to be careful with their size. Great Danes will also need quite a lot of space, yet they are known to be amazing with children and other dogs, so you will not have to worry about that aspect.
You will have to be careful if you are not prepared to say goodbye to them very fast since they are known to not be associated with longevity and they may leave your home earlier than expected.