Soles can be made either with or without the non-slip sole. If I’m making these in newborn size, I usually omit the extra work; however, if you make sizes for cruisers/toddlers and have hardwood/vinyl floors like we do, you might want to make non-slip somehow. I’ve never been good at the glue on stuff to make dots on finished soles. I use thin cardboard templates to trace/cut out my non-slip fabric and then crochet a sole to match, but you can crochet the sole first and then cut the fabric one row larger than the unfinished sole, about ¼”. The final row of the sole is crocheted with the yarn sole and non-slip fabric sole held wrong sides together. Alternately, you can try premade soles like leather or something and I imagine the steps would be more or less the same from a row of single crochet around the edge and moving up the sole sides.