I always go to the Disney site first to figure out what I want and then tell my TA to book it. The Wish is brand new, completely new ship design, still having finishing touches added and no one knows exactly what the rooms will be like, just whatever sketches Disney has out there. 9B should be midship, which is great as far as sea sickness. Looking at a Wish deck map I think deck 2 would be perfect for you, the age 3-12 kids clubs are on that floor! We love sailing 9C aft, deck 2 Oceanview rooms on the Magic/Wonder, so don't worry about being on a low deck, it's really not 'that' low! I will say that right now, Disney has been moving people on deck 2 on the current 4 ships to higher decks and using deck 2 as a quarantine floor as it's close to health services on deck 1, etc. Who knows if they will even need quarantine rooms by the time the Wish sets sail in July. Also, if you have a guarantee room, you are guaranteed a 9B or better...so you could end up in a 9B, or a 9A, or an 8 or something else, you won't know until you get your room assignment which is usually within a couple weeks of sailing.
Enjoy your cruise!