sewing battings together

I was looking at batting and it was rather expensive. I ended up with a 1/2 inch thick bagged batting for a queen/king quilt but I decided it wasn't thick enough. I went back to buy another one (this is still less expensive than the batting bought by sq footage) so it would be an inch thick. Does anyone know how best to put them together? Is it enough to sew them around the edge with the quilt top and backing and then tie them, or do I need to tack them together in some other way?