I'm in Texas so I have the same struggles. It's summer here most of the year. The women here were talking all about puffer jackets the other day and I thought I was going to pass out.
It's difficult for me to find suitable layering pieces but I have found a few.
If you look at http://abie.lookfab.com you can see a few things I've done. Cropped short sleeve cardigan, short sleeve shrug, cotton short sleeve jacket.
I'm just starting to wear some scarves. I have a few that are a really light mesh and I wear them away from my neck a little so they don't feel warm. Light cotton scarves or linen is pretty cool too.
I find that sandals really cool down an outfit. If I'm wearing something a little warmer on top I try to wear open toe shoes. I know that sounds silly, but I really feel it helps.