My wife and I did the Camino is September, and we did not carry a sleeping bag. A fleece bag liner and a silk sleep sack was it. Remember, you will be staying indoors, with a number of close friends whose 98 degree F bodies will bring warmth to the room, even if the room is not heated.
The fleece liner was rated to 55 F and the sleep sack was good for another 10-15 degrees F lower.
Also all the albuges we stayed in did have blankets but the number may be limited, most bunks had blankets on them however.
Buen Camino,
Jerry