I have bought lots of fabric pieces at yard sales, thrift stores, my own closet and closets of some of my friends who will let me snoop around. Try to stick to the same weight and feel and you should be okay. Using your kids clothes, or what is left of them after you recycle to another child, would be a great help to you. Good luck to you and your hubby in this trying time. Hope he will get a job soon. My thoughts are with you.
PS - I have used old flannel sheets and sheets for backing fabric as well. They have been well washed and used and make a very soft backing, and probably will not shrink.