in France, the logis de France group is usually very reliable [with good food too]

https://www.logishotels.com/en/

and for B&B you could try Gites de France

http://www.gites-de-france.com/locat...bre-hotes.html

"Cologne down the Rhine river (Koblenz) to Luxembourg city"

(You're actually traveling UP the Rhine and the UP the Mosel as well.)

I would not book in Koblenz, a mostly modern city, as there are some very charming Rhine towns (Boppard and Braubach) within a few minutes of Koblenz. And if you were planning to just "make a right" at Koblenz for the Mosel Valley, I would first want a little time south of Koblenz anyway - unlike Koblenz and north, THIS part of the Rhine is a UNESCO world heritage site:

http://www.welterbe-mittelrheintal.d...php?id=274&L=3

Braubach is home to Marksburg Castle - a never-destroyed medieval Rhine castle you can tour. Try the Felsenkeller:
http://www.pension-felsenkeller.de/uk/

Other Braubach inns: http://braubach.welterbe-mittelrhein...g/hotels-inns/