I’m a solo walker on the primitivo right now and I have had no trouble finding a bed even when I don’t book in advance. I’m also hearing from other pilgrims that there are often empty beds in at least one albergue per town (usually the municipal which can’t be reserved in advance). Of course many albergues I’ve stayed in (especially those that can be reserved) have been full most nights.
That said, I’m a slow walker and often am one of the last to arrive in town, so I frequently choose my destination for the next day or two and book one, maybe two nights ahead. As I’m primarily looking for dorms, that has never been a problem. If you are looking for private rooms it is more difficult in the busier places (but still pretty easy in the “in between” places).
I have really enjoyed that method because I can keep in tune with how I’m feeling each day and not feel like I’m stuck in a schedule because I’ve booked so far in advance.
If you want private rooms, don’t trust booking.com necessarily as most places don’t put all of their rooms on there. You can call or Whatsapp message most places and reserve a room that way (and usually for cheaper than booking.com).
All THAT said, the next couple of weeks are big holidays in Spain, so it’s quite possible beds will be more and more difficult to come between now and May 22nd, especially in places that are not exclusive for pilgrims.
