At the risk of sounding repetitive, your only option at this point is to handle it on board. Don't stress out too much. Even if the person next to one of you doesn't want to move, there's probably some combination of people in the cabin that will. There are usually lots of people that travel in the business cabin that are traveling solo - ask your seatmates for help once you're on board. If that doesn't fix the problem, as the FA.

Especially if you have to involve a FA, don't mention things like "we booked 11 months out, much earlier than everyone else" - this only works against you. Keep the matter to the fact that you and your spouse would like to sit together, and could they possibly help you in finding solo travelers that are willing to change seats,