I’m a huge fan of how you solve it here! HD=hp is such a swift method. I’ve been using morale = hp for a while, but I’ll swap this in and give it a try.
Oh that's a great idea. And yes I've found that as long as you give a simple 1 HP per HD it seems to work out well (and all credit goes to Into The Odd being so brilliant). I like to add +2 HP to larger foes, as well.