Yeah, minimalism is a hard method to work with. I'd say you're doing well though, try to work with stylized cell shading rather than extra details to mitigate that.
See below for an example of what I mean!
They manage to keep the smooth minimalist style intact, but the details in the fabric folds and the shadow of the hat remain intact even as the details are reduced. Try removing the shading on the windows and wood paneling, working purely with the darks instead!
I'd also reccomend removing all lines from the door and that paneling, it clashes a bit with the rest of the pic's linelessness.