The most important thing is to get him to a vet asap.
Do you have more than one cat? If so, and as he is new, did you give him his own litter tray or is sharing one with your existing cats? Has he been stalked at the tray by either another cat or a dog? The tray should ideally be somewhere quiet where dogs simply cannot gain access to.
I wouldn't get rid of the sofa, but I would absolutely soak the area he's using with a good Enzyme cleaner, enough so that it soaks deeper into the fabric than his pee did As it is quite likely a habit at this stage you'll also need to ban him from the room for quite a while until he is back to using his tray reliably or at least make it so that he can't settle on the sofa, even a couple of sealed empty cardboard boxes (I say sealed so that he can't get into them and pee in them)
I'm going through the exact same thing at the moment. Our Buffy cat is peeing everytime I turn my back on him the last two weeks
Stephen 3 Cavs - Cody, Abigail & Jasmine, Gavin the terrier and the cats - Buffy, Kendra, Thomas, Caleb, Robin & Cadbury, the Geckos - Crane, Poole, Schmidt, Amber, Seven, Eleven, Thirteen, Ivy, Gretchen, Darcy, Ari, Zeva, Claude & Claudine, Alpha, Bravo, Charlie, Delta, Dov, Ronia, Netanya