I think flannel would be a fine choice! I have been making a lot of quilts lately with flannel as batting. They are less bulky when quilting and have a really nice weight to them when finished. An added bonus is that plain old white or off-white flannel is much less expensive than traditional batting (such as warm and white or warm and natural). I do wash and dry (high heat) the flannel before using it as it shrinks quite a bit.