Hello again Kathy. How much of the Camino Olvidado are you walking? if it's a week you will get to about Aguilar de Campoo, as Laurie has said. It is full of accommodation. After Bilbao there is 3 Albergue Juveniles and one Albergue de Peregrinos plus other private accommodation. Some guides show other Albergues but these are only for groups of people and do not accept single person bookings. The information in my guide has all been verified as of October 2018.
I don't normally bring a guidebook but just a list of the villages / towns with the accommodation, supermarkets, bars etc. Similar to the format in the site
[
https://godesalco.com/plan ].
In 20 years of doing Caminos I have never booked any accommodation. This wouldn't suit the majority of people, but I have a good idea of where I'm going to stay that night and 99 times out of 100 I do.
I enjoy the freedom, spirit, adventure, whatever you want to call it, of what the day throws up in going from A to B.
On the Camino Olvidado last year I took a a mobile phone with me for the first time, mainly for the mountains, in case there was a problem, but as you probably know It is sometimes very hard to get a signal.
In saying all that I've never been in Spain in July or August, In the peak holiday months (for Spanish people ), which on some of this Camino will be busy with hikers etc. So I anticipate the albergues , in the more scenic places, will probably be very busy. Therefore I recommend you to book your accommodation.
After Aguilar there are lots of Parish Hostels (Albergues Paroquial) where, you probably know, they cannot be reserved plus other private accommodation.
Suerte, Mick.