Welcome
@L B. If you have a 40L pack yet no room for a sleeping liner, you might want to shed some weight before you start on the Camino. You can send a box ahead to the Correos post office in Santiago, or Ivar here at this Forum:
http://www.casaivar.com/luggage-storage-in-santiago-de-compostela/index.html.
And like others, I'd recommend having a barrier between you and the albergue mattresses/ albergue sheets. A hospitalera was telling us recently that the two albergues she served at didn't have a policy of cleaning sheets daily. One had their hospitaleros wash sheets every four days, and one had their hospitaleros use a ruler to scrape off the sheets between washings. Apparently they expect pilgrims to be carrying their own liners and sleeping bags and not to sleep directly on the beds.
Enjoy your time. Buen Camino!