Slippers on two needles

Option 1 - Cast on stitches and knit in garter stitch, then bind off a few stitches and alternate  2 rows of stockinette and garter stitch, this will be the middle, and then increase the number of bound-off stitches and continue knitting in garter stitch

Option 2 - Cast on the height needed for knitting to cover the leg, then bind off half of the stitches, knit 2 knit, 2 purl, to the end of the foot, bind off, sew to the other end of the knitting, fold in half, sew the bottom, gather the top