Genius slipper design where you knit a short "scarf", fold and sew onto your bottom. Garter stitch extra chunky yarn about wide, and however many rows you need, then sew into the 2 layers of the felt bottom.
Silfurfit Old Norwegian Knit cast on aka twisted German by Garnstudio Drops design. A cast on that gives a sturdy and stretchy baseline of stitches. Perfect for the top of socks, edge on hats or whenever you want very stretchy cast on.