I have this gimmick for my next campaign and I’m looking for advice on a campaign to run it with

The gimmick is that none of my player characters can choose a conventional race. Instead, they choose some sort of mob and we’ll work out some PC features for it. So far they’re enjoying the process, but I wanna make sure I’m running a campaign that might complement that idea

I’ve looked around, but would anyone happen to have ideas of any campaign book that you think could complement this whole “band of misfit monsters” bit??