Actually, I would really like to find a similarly non-bland proportional character to use beside it.

Well, there’s Fira Sans, but I don’t know if it’s what you want. I like to use it for things like slides and titles, and I’ve used it as a GUI typography for some time.

I use Fira Code Retina. I like that it is not too light, not too bold. I’m also partial to Cascadia Code and DejaVu Mono.

For the GUI, I use Adwaita Sans in both my GNOME and XFCE computers.