For the type of climate you are describing, and for the hand quilting, I would probably recommend Quilter's Dream Poly. It has gotten many favorable reviews here, is lightweight, and machine washes easily. Maybe Google and search here for more info on it. This is not a batting that I personally have used, but it seems to suit your needs. My second choice recommendation would be Quilters Dream cotton request weight. This is good for hand quilting, would not be too heavy or warm, but gives a somewhat flatter appearance to the quilt.
My favorite battings are Mountain Mist Blue Ribbon 100% cotton, but I do not recommend it for hand quilting because of drag on the needle. I also like Hobbs 80/20, and that would be my third choice for you. However, I think it might be overly warm for your climate. It's a nice soft batting with moderate loft and is easy to hand needle.
I personally would *not* use Warm and Natural. It is needlepunched through scrim, and the scrim makes hand needling more difficult. Also, it is a dense batting that may not be suitable for your climate, and it is a stiffer batting that does not drape as well as the others mentioned.