Fixed to get in the last two heritor feats (thanks!).
I have been looking, and can't find any feats that make stat-switching mandatory that don't also require me to have levels of monk or paladin, neither of which I am allowed, unfortunately.
Druid avenger is a good call, if only I could cheat my way into frenzied berserker or if there was another way to make rage mandatory, which I've been as yet unable to find.
Armor proficiencies, alas, don't count, because wearing it isn't mandatory. Hmmm... mandatory armor... warforged! I can take adamantine body and instantly lose... well, basically everything druid-related!