accommodation planning on-the-fly in Netherlands to Provence, France

I am planning a multi-week, Netherlands to Provence bike trip in May
(or maybe the other way around to give the weather a chance to catch
up.)

I am getting some excellent suggestions on equipment in another post
but now I turn my head towards sleeping arrangements. How best to
manage 3-4 weeks of probably on-the-fly sleeping.

Camping is out; rather hostels, gite d'etapes and cheap hotels are
planned. But I do not expect to have the route so tightly planned that
I can know where I will be everyday or night (so as to pre-book
accommodation).

I can imagine myself either at 8am starting to think "where should I
head to today" or at about 3pm wondering "where might I expect to wind
up today" and not have a place to stay figured out yet.

Does anyone have any tips on how best to plan accommodation on the fly
like this, between 3 hours and 3 days in advance? I cannot seem to find
a really good website with a map that I could use to look a day or two
ahead as I was pedaling. I am remiinded of the Forumle1 chaiin of
hotels which do seem to be almost everywhere in case of emergency. (but
30+ euros a night, while cheap, would start to add up.)

any tips?