The word "couchmate" refers to a person who shares a couch or seating area with someone else. If you are looking for synonyms for this word, there are a few options to consider. One possible substitute is "seatmate," which can be used to describe someone who shares a seat with another person. Another option is "sofa companion," which has a similar meaning to couchmate. You might also use "couch buddy" or "furniture friend" in place of couchmate. Overall, there are many different ways to describe someone who sits or lounges alongside you, depending on the situation and context.