Wendy, it may be worth checking threads about light layers, as opposed to bulk. Perhaps as well as some craftily calculated layers you might want to take one piece of extra clothing that is old but servicable, and which can be discarded.
I say this because in May of 2010 the weather got very cold indeed on the Chemin du Puy, even where I was by that time, in the Bearn, where it should have been warm and radiant. Even in late May there were widely reported weather probs in the Pyrenees.
One simple but sometimes overlooked tip is to wear everything and carry nothing in the cold. Also, stay dry, and treat your rainwear as yet another warmth layer when it's not raining.
I always walk in the colder times, and my next camino will involve some layers of Heattech or Icebreaker, a decent jacket, and my old-style (not clingy new style)
Altus. If I have an underlayer that I want to keep clean, I'll wear it as a mid-layer. And there'll be one old rag for chucking as the weather warms.
Just some ideas, pretty incomplete, maybe too obvious, but I thought I'd mention them. My slogan: If it's not a layer, it's an at-home stayer!