It’s always a good thing for new fans to get to know the older stuff. I find it interesting that a lot of people mention GIRL FRIENDS feels kinda dated, cuz my impression (when I read it 5 months ago) was that it feels surprisingly pretty modern, and also more realistic than a lot of more recent yuri
青い花, 君と綴る, and やが君 are all on my “must reads” list (I mean nobody has to, but I think they’re all excellent and unique). きにおと is also great. Good reminder that I should rewatch 青い花 anime 
That is one of the Class-S (and Related) Reading Club - READING 乙女の港 nominees, and we’ll probably have our next vote pretty soon fwiw. 青い花 is also on the list.
That said I’ve watched a bit of a 朗読 playthrough of flowers. It’s pretty cool, but also not the easiest. Actually it was pretty affirming watching the reader frequently look up kanji. Now that I think about it, I should check if any of the vocab seems relevant for 花物語 上 | L39 (or just start making an anki deck out of that I guess)
Interesting premise & cover art
That’s an interesting twist
Hmm the only one I know is UsoNatsu. It’s easier than flowers at least, but idk that I’d call it easy (tho I’m not that far in)
