If the cat stays on the couch then your puppy thinks he has the right to do the same thing. I think what you are trying to do it's a little bit unfair for him. But the good news is that your dog is still young and you can still train him successfully to do as you please.
Buy a new cosy bed for him and put it next to the couch. Or maybe a soft blanket, dogs love it. Get some new toys and put it there too in order to keep him distracted and entertained. If he jumps on the couch take him down, put him on his bed, but act gently. Do not raise your voice, do not scare him. All you have to do is to find something more interesting for him than the couch.