I’m in just the same position. We have continued to cruise on Royal Caribbean. My son (10) loves the smaller ships as much as the big ones, he might visit adventure ocean a couple of times if they are doing science or something but I’m happy if not. We do lots of the free stuff on board like napkin folding as well as one or two $$ bits like the sushi class or cupcake decorating.
We take travel games for evenings or bad weather and spend lots of time in the pool. Scavenger hunt is always good fun and adventure ocean usually have a family activity during the day at some point.