It wasn't all that difficult, but as with all new things, it took me a while to get the hang of it.
I'm not sure how well this works at keeping the slippers non-slip. I'll have to get back to you on that, after the recipients get their long-overdue Christmas presents and try them out.
In case you'd like to try this yourself, the tutorial for this method is found here. I googled "soles on knitted slippers" and this site came up.
As you can see, her soles look much, much better than mine. I used a faux leather fabric.
Ah well. It's done now. Would I use this same method again? I don't know. It depends on how well the slippers work out.
And with that, my Christmas 2018 knitting is done. Christmas 2017 knitting is still ongoing.
Bedroom deluge update: I still have a big ol' hole in my ceiling.
It's pretty much the entire ceiling. It will not get repaired until the restoration company knows who's paying to have it repaired. The owner of the property upstairs refuses to pay as does her insurance company. The renters still deny that anything whatsoever actually happened. So, before anything else can happen, we have to take them to court. Ugh.