Should I buy art to match the couch. Many people do!!! But try to think outside the box. One might make a collection of small works that look great in any one space even over the sofa. One large piece over the sofa isn't necessarily the best aesthetic. Be creative and if arranging a room is not your best forte, find someone who can lend a hand. You do not necessarily need to hire a decorator. Ask a friend whose style you admire to help you out. There are plenty of books and information on line about space, size and proportion relationships and color. Think of a large sofa and think of a large painting over it. The comparison might be like two big boxes lined up. Consider trying other options. There are plenty of decorating magazines to give you examples.