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
this would be easy to do without a pattern, make first row as long as needed then decrease every other row until you get it as short as you'd like for the arm length and the wrap around the back, then just repeat for desired length. Easy to CROCHET, too!