I bought a pair of slippers soles for a 2yo and calculated my size and stitches from the soles and my gauge. I couldn’t find a pattern for what I was envisioning, so I made this up myself. There was a ton of frogging involved in the process.

Steps:
I crocheted a round through the holes punched in the soles.
I picked up and knit enough stitches evenly from my crochet round.
I created the ridge by picking up sts from a prior row and knitting together with the current row, placing 1 row of contrast color in the ridge.
I knit the top of the foot back and forth with German short rows.
I created a purl ridge around the ankle to pick up later.
I made a k1p1 rib cuff, binding off in Kitchener st.
I crocheted a decorative crocodile st cuff from the purl ridge, outside of the ribbed cuff.
The crochet cuff is loose enough to allow the slipper to be slid on, while the rib cuff is fitted to keep the slippers from falling off.