I think there are several books, quirky, I know there's a specific one written for MH professionals, some sort of practical guide/workbook type thing. I've only ever read the main one.
I agree snowflake is a terrible term. It just struck me why people who are otherwise unaffected by it would be so annoyed by it. It's very counter for an HSP to go round proclaiming any special status or demanding special treatment for it. I only ever mention it when I spot a fellow HSP and only really in case they're unaware and it's just nice to pass on the mental clarity you get with understanding it all. Otherwise really only with someone you're very close to and it matters.
I'd forgotten about Aaron's obsession with Asian culture, though I do feel she paints a far too rosy picture of it. But it is interesting, there's a show on Netflix, Terrace House, which is reality TV from Japan but it's the polar opposite of Western reality TV. It's very slow and everyone is quite considerate of each other. Drama is noticeably absent. Men cry all the time without that being seen as weird. It's really interesting to observe, although there are some things that make for more difficult viewing from a Western perspective.
Since we were talking books earlier, it's a bit marmite but I absolutely enjoyed it at the time (despite seeing the twist well before reveal), We Are All Completely Besides Ourselves by Karen Joy Fowler. Not advertised and I doubt intentionally written as such but it's a good insight to a child HSP's experience.