Couldn't link it earlier was on phone, here you go. (scroll down to the bottom)
http://september.strawberrywine.org/active-projects
Volume 1 is also a movie, but in my opinion the novel was better. Not that the movie was bad or anything, but if you watch it, I'd definitely go back.
Also, the novels are fully translated here ( https://ytnb01.pressbooks.com). There are six of them, so to get to the others just change the number in the link, or google it (should be the first result~)
As for the omakes, 1-3 are here, 4-5 are on youtube, and you have to download 6-8 here ( http://september.strawberrywine.org/archives/category/sekakoi/trifecta)
There are also some short stories that weren't included in the novels.
I'll dig for it later if you're interested (〜 ̄Д ̄)〜
Yeah I remember Kirishima being introduced and pieces of Yokozawa's story so I must have watched the movie at some point (didn't remember that though when I was reading the manga so I was very confused XD) I just assumed that their story was included in the manga but apparently it wasn't and that is okay because I can go and read the novels now (●'◡'●)ノ
Am I hallucinatingXD where can I find the whole story of Yokozawa Takafumi no baai or does one even exist? I would appreciate any info about the matter