Hi Hellie, welcome to the forum. Last year I took just a sleeping bag, down filled, in September on the Le Puy Camino. It was too hot for my sleeping bag most times, but I used it anyway. This year, I'm doing the Frances, same start date as you, and I've decided to take my sleeping bag AND a cotton liner. I'll use the cotton liner if it's hot, and my sleeping bag if it's cool and both if it gets cold. I found the liners were quite expensive, for what they are, so I made my own. I just bought some fine cotton fabric and stitched it down the sides. It cost me $26 AUS. It is extra weight to take both, but I figure I can always ditch the liner if I don't need it.