Wool batting makes a very light, but warm quilt. When I want a white background I ask for the fabric the quiltshop calls "snow". I have used it
with the 30's reproduction fabrics and it looks great. I think most quilt shops or online shops would know what I mean. Good luck. It is a very pretty pattern. I agree that sometimes it is hard to get all of the seams to match, but perfection is not everything. Making the quilt for someone you love is the most important thing to think about. I have used muslin many times for the back of my quilts. I love to be able to see the stitching on the back and it shows up well with muslin. Buy a good grade of muslin though because some of it can be pretty flimsy.