I also use a light weight batting behind my embroidery piece, I am a hand stitcher and find it much easier to work with this way. I do not always use muslin, sometimes I use a tonal piece of fabric that relates in some way to the design I am stitching.

I don't believe you would have a problem with using muslin as a backing on the embroidery. When I was making dolls with embroidered faces, I just used a piece of interfacing, which took care of any "wandering" threads.

Just a few days ago, I posted pictures of my "Over the River and Through the Woods" quilt....Believe it or not, I did my embroidery on cream colored muslin with no backing whatsoever, and I had no trouble with it at all. Was very easy and pliable to work with. And, it quilted up just fine. I was a happy camper with my quilt. Just my two cents. I read the directions, but just decided to do it my way. Might not work for everyone.

The first time I saw this was a vendor at a quilt show and she used flannel. Old timely "inexpensive" flannel and the needle goes through like butter. I recently used muslin scraps from my stash and some of it needles with some difficulty. I'd you try the flannel get sure it is old type the same on both sides not the newer ones with a rayon type backing. I think it adds substance to your embroidery and helps make the knots and traveling stitches less noticible.

I used to use muslin on the back but now use a thin white flannel. Try it, you will be happy with the results. The flannel also hides any thread you might use to move onto a new section. Good luck!