We were warned that a river cruise is nothing like an ocean cruise, and people that did not understand that in advance were disappointed. We did our research and were prepared. We knew they were two different things - just like a camping vacation is different than a resort vacation.
We had the time of our life!
If you're thinking about a river cruise, then I presume you will look into what it actually entails (and doesn't) so I won't reiterate that here. All though I'm happy to respond to any specific questions anyone might have.
What I will share with you is Gate 1 Travel. (Since Rick Steves doesn't offer this type of service, I think it should be okay to recommend another company.)They were recommended to us by my aunt as I had serious concerns about using the big company that advertises everywhere and that everyone has heard of. They own their own brand new ship (ok, it was one year old when we were on it in May 2018).
Again, I did my research and was impressed with what I found not to mention the price was substantially lower than the Big Company. I made all the reservations online and handled everything electronically. However, they do have a customer service department if you prefer handling things that way.
We met many people on our cruise who have taken multiple trips with Gate 1 in different areas - and to a person, they all raved about their experiences.