NOTE: This option has been tested down to 14C, but with clothes on, not naked.
Snugpak makes the, "Jungle Blanket," about the size of a double bed or an unzipped sleeping bag, or liner. The Jungle Blanket is like a, "lined," liner, which I have found to be perfect for Summers on the Camino Frances
. It is small and incredibly light yet gives you enough to keep the cool evening temps off and promote relentless slumber. And it comes with its own compression bag.
Using even a light sleeping bag on this trip can find you perspiring in the middle of the night, creating discomfort and waking you asking yourself, "Why am I drowning???" The Jungle Blanket breathes and as it does not overdo its insulating feature, I rarely found myself overheated.
My blanket is about 2 years old now and it gets a lot of use. Fortunately, the material is antibacterial so it takes a lot for it to start to smell. This is great for Peregrinos as we usually have to pack up and get out. Airing it out with laundry works just fine.
Now, I just looked up costing on these and got a surprise. I got mine on sale for about C$25.00 but now Amazon Canada is looking for over C$80.00 for them. Do your research. Find a deal and leave the sleeping bag at home.