I use Quilters Dream Request for most of my machine quilting. In fact I get it by the large roll.
I also like to have some kind of batting or filler inside the quilt. The thinist I know of is Hobbs Thermore.
It is soft and drapabale, gives just a bit of loft for your quilting. It is packaged in various sizes.
I believe anything else (flannel, fleece, etc) will add unwanted weight to the otherwise light weight quilt.