I agree with the advice above about consulting a TA.

I've enjoyed my river cruises with AMAWaterways. I've typically sailed with a group of friends with a wide variety of interests and activity levels, and AMA has worked well for all of us, offering bike rides and hikes for the very active, while I didn't feel like I was left behind in the gentle walkers group. There is no requirement to stay with the group at all, plenty of free time to go off on your own.