I would not claim to be able to recommend any specific books as I don't know much about you. However, I have travelled a lot and my wife and I are currently away on a 4 week or so cruise on our yacht (which we do frequently), so I can give a little glimpse of the characteristics of the books I read.
Generally, I find that shortish and lighter books that can be picked up and put down quickly without loss of train of thought are easier to manage because of the unpredictable needs of mingling with other people, outings, longer meals, etc. I've even taken the opportunity to read through light short "easy" books in a series that I would not normally pay much attention to.
In the case of on boats I have to manage ours which is a considerable interruption to longer reading sessions and concentration, but one assumes that if you are going on river cruises you will have the interruptions of changing scenery, stops ashore and of other passengers (especially if the number of passengers carried is not large and so likely to form a more garrulous group). When we have friends who read sailing with us they generally seem to find that the only solid reading time is for a short period in their bunks at night before sleep overtakes them.
Of course, if one is travelling alone and going to keep to oneself, all the above is irrelevant
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