have you ever read This is how you lose the time war? I'm considering reading that one next

Just finished it and I love it. And it actually fits into the genre I mentioned above really well.

Lesbian sci-fi? Check. 2019? Check. Debut? Kinda - seems it's the first novella of one of the authors. There are two empires, even though they're not called that. It just didn't start a series, so I guess I'll drop that part and list it as one of three books that fit the rest.