Not sure what you mean by heavy. If thick is what you are looking for, I use two layers of wool batting from Taos Mountain Wool Works
http://www.manta.com/c/mm4xmz8/taos-...in-wool-works. They do not have a website. I've used them since before wool batting was widely available. Quilting through that batting is like quilting through butter. I've also found basting very well and keeping quilt very loose in hoop helps me make smaller, more even stitches. Actually, my biggest problem is seams, not thick batting- unless it is poly or worst- cotton.
Maggie