Spending the night cold will wreck you for a few days. I spent many nights cold while trekking from Mexico to Nicaragua; not something to reminisce about. I also got cold canyon climbing in Utah, not to mention the hundres of cold night camping out in the US and in Canada my home country. There is nothing worse than having a bear, coyote, wolf, racoon, or squirrel sniffing or scratching about with your nose dripping. I've over 2016 and 2017 trekked Le Puy, Del Norte, Primitivo and part of the Frances. With 850 dry down it is easy to get a lightweight, warm, comforter type of sleeping system. An ultra lite short air mattress will keep you off those cold surfaces to include the cold blue rubber coated mattresses that are the norm in albergues and gites. Many of the Compostelle or Camino trails cross high altitude areas where you might not have much choice where you will spend the night. If you aren't ready for that, you will suffer. Some of the albergues and gites are not heated. After spending a couple of miserably cold nights you will probably spend twice the value of a high quality sleeping kit on a hotel. Skip the hotel bit and get a guaranteed good night sleep. And that's my last off on the subject.