You need to get your dog a special “couch”
Okay, you don’t have to get your dog an actual couch, it can be a dog bed. But get them the comfiest, biggest, snuggliest dog bed you can find. You want your dog to feel bad for you that you don’t have such a cozy place to hang! It can live right near your couch. In fact, it is probably worth investing in one for each room where your dog likes to spend time.
For a few weeks, feed your dog their meals on or near this new bed and whenever you leave the house, sprinkle some treats on it and around it. If you happen to catch them lounging there, praise them wildly and give them a treat or something yummy to devour. Sometimes, take a minute to play and snuggle when they’re there since part of the interest in the human couch might be that they get to be there, some of the time, with you.
Make the human couch unappealing
While you work at encouraging your dog to like their bed, you want to work at making your couch unappealing. Whenever you’re trying to discourage a behavior by altering the environment, it’s smart to start by using only the mildest deterrent possible. This can simply mean physically blocking access to the couch.
If you’re going to allow them to have access to the couch when you’re not around, put something in the cushions that will make them less comfortable, but that will be out of sight. Tinfoil inside the cushions might be enough, or you could try a piece of cardboard. If those don’t work, experiment with plywood in the cushions, or some rocks, or even just make it really lumpy by putting some stuffed animals in them.
You won’t have to live with your sofa like this forever. I’d just do it long enough so that your dog starts to feel sorry for you that your couch is so much less comfy.