Hi,
@elajenki, and a very warm welcome to the forum! You’ve asked a question that is on the mind of a lot of people as they prepare their first camino. You are going to get a lot of answers and opinions, in fact you can see a
thread from almost exactly a year ago discussing the same question.
Before the strong opinions start rolling in, I just want to say that imho the only thing any experienced pilgrim can tell you is whether THEY will need a sleeping bag. This is not a question of averages, of going with the majority, it’s a question whose answer for you depends on your body and nothing else! I have a little soapbox post that I like to insert in these threads:
I think the "should I take a sleeping bag" question is the same as the "what are the best hiking boots" or "which backpack should I use" questions. This is a question that no one else can answer for you because it depends exclusively on your own body. I don't doubt that all of the posters have accurately reported on what feels good for them in those conditions, but they have their own unique internal heating and cooling systems. I always take a lightweight sleeping bag (850 grams), even last year arriving in Santiago in late July. But then I'm what the Spanish call "friolera", someone who gets cold easily. Only you know if that describes you too. If you're the one who always pulls out a sweater to warm up in summer air conditioning, or who needs extra layers when sitting around in the winter, then you will probably be very happy with the decision to carry a sleeping bag. If you sweat a lot and run around the house in shirt sleeves in winter, then you are likely to be fine with something much less.
I think you will get a lot of opinions, and there’s nothing wrong with people sharing their experiences, but I think the best thing for you is to go with your gut feeling about your own body temperature.
Buen camino, Laurie