This sounds like a great adventure. The sites/monuments in Paris are spread out and not clustered in a single area (as you might expect in a modern American “downtown”), so it’s difficult to answer your question without more information. Many of us could rattle off hotels that we love and areas we find charming but this is your trip! To maximize your brief visit, to see and do what’s most important to you, it may be of value to do a bit of research to find the area of Paris that interests you most. If you haven’t already done so, I’d take a quick look at a guide book or two - Rick Steves’ Paris is a great start. I also like DK Eyewitness books for the great photos and quick descriptions. You might be able to get these from your public library. Once you find the place/area that sparks your interest, I’d look for hotels in that area. You also might prioritize convenience of getting to your embarkation point for the cruise.