Hey Bernadette. Easy to second guess ourselves as our Caminos get closer and closer. A very natural part of the preparation process.
@Peterexpatkiwi identifies the many parameters that determine sleeping comfort. More than likely, several can be applied to any given night on the Camino.
Eight years ago, and I walked primarily in May, I decided to take a lightweight, one-season sleeping bag. Now, was it expensive? Not sure. It cost around $100, but I have now been using it, on and off the Camino, for eight years, so it seems to me like a pretty good investment.
Because I would always err on the “I’d rather be warm” side, carrying a 17 ounce sleeping bag seems like a good choice. Secondly, I ran into enough chilly or damp nights that the bag was a most welcomed companion at night. Conditioned varied greatly albergue to albergue. Some albergues offered blankets, others didn’t. Ventilation varied greatly from one place to another. As I had a designated set of sleeping clothes, I really didn’t want to add other layers just to stay warm.
In June, a liner might be adequate. However, I’d like to have the option of smuggling into my mummy bag or sleeping on top of it. Regardless of your decision, it’ll work out fine for you and I’m sure you’ll have a great Camino.