How will you be hanging it on the wall? If you are framing it, it may not need backing or batting, you can put it around a piece of cardboard just like a needlepoint and stitch tight in big stitches across the back. If you want a display piece, I do agree with some sort of something in the middle. A piece of white flannel (prewash hot and dry hot first) can be just enough.
Sometimes a wall hanging needs a little curtain weight or washer or something in the corners to help keep them down and in place.