This pattern is for knit slippers, but I can totally see using a wool sweater and cutting and serging slippers from it! Home Slippers - DIY. this is knitting, but I bet I could use this to crochet some
Knitting Tutorial: Joining Stitches In the Round with a neat, easy and invisible technique. Just make sure that your stitches are not twisted on the needles before joining. GOID Idea for joining in the round Should be a better join solution.