If you’re going to decorate your sofa with cushions and you like large ones, the basic rule is to put one cushion more than the number of spaces that the sofa has. So, for a 2-person sofa, put 3 large cushions. If you prefer small ones, you can use more, but bare in mind to stop before the sofa becomes uncomfortable. In other words, if there are so many that they practically don’t fit on the sofa, you have a problem with quantity. And remember, it’s better to have a few, well-chosen cushions, than many placed any which way.