I can't help on the topic specifics, but I can recommend a tool. I don't know if your DS' interest level exceeds the upper range for this idea, but one database I like to use when finding resources is called "NoveList K-8 Plus" (there is an unbounded follow-on, otherwise-- "NoveList Plus: Your Guide to Reading"). These give you keyword, theme, and tone targets (as well as level) for fiction and non-fiction. We have both of these available free through our public library.
If your local library doesn't have these services and they're of interest, PM me.
I've used them to find some really niche media.
