I came across this topic of discussion regarding places to stay while I was doing my own planning for next year as well.
As we all know there are many accommodations that are family run small businesses along the way, most of which do not have an internet presence and rely solely on word of mouth recommendation(s) and/or Pilgrims coming upon them once in town.
I have been trying to use as many (English printed) online sites as possible to make my plans and recently began using Google maps as a tool in this capacity.
While doing so I have learned (I am a dinosaur with computers) I found when researching a particular city on Google maps on the uppermost page there appears a prompt labeled "Hotels". I find when I click on the prompt a host of accommodations pop up with various prices and locations indicating to me that these accommodations are already on Booking, Priceline, Trivago etc... That is the obvious and easy part.
What I also found though is that, if you look closely at the attached photos, there are numerous small unlabeled dots in the photos. These are usually small accommodations within the area(s) of your initial search, which are NOT being represented by the big booking companies and can be reached usually by phone or by the owners personal Emails (My experience on at least two contacts thus far).
Yes, it is a lot of work pre-planning a trip of this duration, but as all things in life the sweat must be put in before we can reap the gold of our efforts.
(The city used in this example is Reims. The photo on the left illustrates the "Hotel" prompt at the top of the page. The photo on the right is the illustration found AFTER one has clicked on the "Hotel" prompt from th first page/search. Note the many unlabeled dots on the page. Hover your mouse over each and it will provide the name of the location/accommodation. Good luck!)