I've fused a quilt top to cheap muslin before (the quilt top was very old fabric with issues so it needed more structure & I didn't want to dye stabilizer to match). I used Pellon 805. It turned out fine. In the future, I'd probably go with Misty Fuse instead because it has more movement, but honestly, after it was washed twice, the 805 softened right up. I quilted mine with a 70/10 Microtex needle and Aurifil 50wt thread because the holes will be more evident with the muslin fused to it unless the thread completely fills in the hole. With fusible, the holes do not shrink closed as readily as they would with regular quilters cotton or muslin by itself.
Also, unless your quilt top is mainly bright white, I'd probably go with a natural colored muslin over a bleached muslin. The white will show through a bit if your top is either off-white or pastel colored. Finally, this is the one time where picking the absolute thinnest (cheapest) muslin that JAF sells is the way to go.