I have only walked theNorte from San Sebastian to Llanes, and did look for shorter days, but short was low 20-23km a day, and even then it was tough.
While the Norte has seen a lot of Camino development lately, it is still limited when it comes to albergues and other overnight options. This is even more the case outside outside of June to October.
If the Frances was a physical challenge, please do study guides for the Norte carefully.
What you may have to do is rely on taxis to go back and forth and do half etapas: leave your pack in the morning in the albergue, walk x number of km, take a taxi back to the albergue, The next morning have a taxi take you to where you stopped the day before and coml,ete the etapa. But this will take planning as you will not be passing by cafe after bar after cafe from where to call a taxi and may have to decide on a meeting point and time the evening before.
Super tough daus are the first out out of Irun, the day from Deba to Markina, (there is a bus stop in Munitibar to break up the day from Markina to Gernika).
Again, get a good guide (if you read Spanish, I really recommend the ine by Editorial Buen Camino) and try to see how you can break up etapas. Look into hotels, pensiones since albergues are still relatively few and far between (but since you would be sharing a room the cost would not be much higher than staying in albergues and juveniles).
It's a beautiful Camino well worth the extra planning.