Misty Fuse is definitely the least stiff. I source it from Amazon. Also, be sure to window your fabric. Here's how:
https://www.youtube.com/watch?v=r_m84NtcyUk
Honestly, though, I usually just get Pellon 805 Wonder Under at JAF & never get complaints because I wash twice before gifting it. The thing that makes the most difference in stiffness in my experience is the thread build-up from satin stitching. I do a 1/8" blanket/button hole stitch.
PS- I've never used it personally, but I've heard Bon-Ash 007 Bonding Agent is even lighter. They are crystals that you sprinkle on fabrics. I haven't tried it because I don't know what's in it & I wonder if it is more difficult to achieve perfect bonding with it. I can't speak to that one way or another. I have had many happy (high end) baby quilt customers with Pellon 805 so that's what I stick with when if I'm using fusible.