I'm still noodling with that Bright Young Things meets Buffy idea; to that end I've been reading books written in the 1920s. There were 3 mystery authors I read as a young girl that fit the bill: Agatha Christie, Dorothy L. Sayers and Ngaio Marsh. I figure how better than to get a feel for the time period than to read it.
There are some issues though. Writing styles can grate a little lots of dialogue tags we simply don't use any more, lots of people ejaculating all over. And then there's the casual racism of the time. I haven't reread Marsh yet (harder to find) but I will say Sayers does better than Christie (sorry Dame Agatha) I did just fall over a descriptor in a Lord Whimsey novel 'as yellow as a Chinaman's cheek' yikes! Christie doesn't seem to like Italians. We do not come off well which WAS par for the course for us in the 20s.
WHich brings us to the what to do with the racism in modern written historical novels. Unless that is somehow the point of your book, you're probably not going to want to lean heavy into it. It's much harder to find examples of diverse characters then so it's harder to see how they would be handled.
We know the reality is the answer is Not Well so we have to put in a little distortion of that ugly reality. 3 early 20th century tv shows I like have done that. Miss Fisher really doesn't have any diversity just a few side characters that are PoC. Frankie Drake has her best friend being a Black woman which probably was a hard thing in those days. Murdoch Mysteries is pretty much a steampunk fantasy at this point and does touch on the racism (and homophobia) of the time but has a Black detective, a Black lady coroner and a gay detective as well and uses them to explore the themes.
There isn't any easy answers. What I've learned is I don't like Lord Whimsy as much as I remember and I rather prefer some of the edited Christie tv shows better. Sacrilage I know.
Have some links
From around the web.
Root Out These Five Writing Mistakes Before You Publish Before They Had Pulitzers How Flawed Characters Create Meaning In Story 10 Tips For Creating Your First Children’s Picture Book (a lot of shilling her book but the actual talk is good)
From Betty
Cure Your Inner Frustrated Writer6 Factors to Becoming Super Productive How To Prepare For A Book Series Traditional or Indie: Benefits of Both How Constraints Help Us Achieve More How to Fix Passive Voice How to Write Believable Children in FictionChoosing a Follow-Up Strategy for a Popular Story Which Descriptive Details Are Excessive to Readers? Relationship Thesaurus Entry: Enemies How to stop writing a novel Want Success? Get Back to Joyous Writing