I know many use warm and natural, but is not your best for handquilting. In fact Jean Brown says not to use warm and natural. Actually polyesters or wool are the best, but if you have to wash the wool, it can be a real problem. But I just recently started using Tucany cotton, it is the softest cotton batting I have seen, it is a new line by hobbs and I love it. They also have it in polyester, wool and silk. I get mine from the Batty lady. She has it on sale right now. This is her site and she has a lot of info and will email you back if you have questions.
http://www.battylady.com/