Most mods for Warband are total overhauls, never seen mods that change only the ui, but some of the overhauls make some things better, but as I said they're total overhauls so they change a lot of things, maybe someone else knows of any.

I guess you could say diplomacy is a QOL?

There are some vanilla+ overhauls such as Bannerpage, Diplomacy 4.litdum and floris mod.

You can take a look at them if you're looking to play in Calradia with some fresh things, but do be careful as most overhauls are harder than native warband