I use Pellon 830 pattern paper, available at JAF. If you have any lightweight or featherweight interfacing lying around, use that. You could even use a lightweight fusible—just trim it about 1/2” from the seam after you turn it and before you press it. This is the appliqué method illustrated here:
https://youtu.be/tqOTaOsWWG4
The difference is that you sew the interfacing to the background, turn it, lay it over the focus fabric, and topstitch it down.