I've looked at barges - there are a few companies that sell by cabin as well, so you don't necessarily have to do a full boat charter. Alas, that means you could be on a quite small vessel with very few people -so if you don't get along with someone, could be an awkward trip. I love the smaller sizes of the boats and the places you can travel, but being with only 2 or 3 other couples I don't know could be challenging.... But at the same time, I have no desire to do a self-driving barge (way too much work for me at this stage in my life ;-) Might try to do a friend group in a few years.....

Back to the OP - if you're on the fence about options, you might consider looking to an affinity group trip - many university alumni associations do cruises, including river cruises - might find a trip with a topic that interests you (in Europe, art, architecture, music etc - then you'd likely have a professor or two traveling with you and special excursions during the trip). I'm sure there are other "hobby" affinity groups that arrange such trips around those hobbies.......