I just got back from a 4 day Wonder sailing. I went solo. It was a terrific experience, I absolutely loved it. If your son's off doing other things, you can enjoy the Rainforest room, sit at the Cove Cafe with a nice cuppa, go to a martini tasting (or wine, if that's your preference), take a galley tour, see a movie. I found sooo much to do around the ship, that I was having to make decisions as to what to do!
They do have a single/solo meetups, however I poked my nose in and didn't see much of anything going on. There wasn't even really somebody there trying to organize it. I found it fun just talking to people around the ship, and ended up hanging out with a single father and his daughter for some one of the shore excursions.
Interaction btwn staff and patrons? Ummm...it depends on what kind of interaction you're talking about. If a CM isn't busy or on their way someplace else, they'll stop and talk to you. However anything more than that is pretty much frowned upon.