Your clogs look great! They are way too much fun to make—and quick! I've made them for everyone that wants a pair in my family, but it's not enough. I want to make more! The hardest part of the pattern is the second row of the sole IMHO. Be sure and count your stitches after this one! I love how as you're knitting the upper part and you come to the slipped stitch you know whether you've done that row correctly or not. The first pair I made I got off a bit...
I've done all mine with Lamb's Pride Bulky (one strand) and they've all come out great. I have started making them with a higher cuff as I find it more comfortable.
You can add soles for gripping if you like, but I like mine kind of cushy feeling and once you put any kind of rubber or leather sole on it makes them less cushy. You can buy soles from Fiber Trends that you can sew on, or any shoe repair shop can put a sole on for you.
I made my 80 year old Mother a pair. She lives by herself too, but I made her promise to change into something different when going down stairs since she didn't want a sole put on them.