I use 100wt silk for my needle turn applique my personal favorite. I use floss for the buttonhole stitch. I have also used bottomline thread from YLI. I think Aurifil 60 wt 2 ply cotton would work as well. The thickness of the thread matters as the wt will not sit flat in the seam edge as you turn. Is there a specific reason that you want to use floss instead of thread for the applique? When I teach applique I show them how to use the silk and then let them use what they want to it is your project. You are the one you have to please. Luann