Debian sounds like it would fit you pretty well. It's a precompiled distro that's package managed via apt. KDE works just fine on it and there's probably all sorts of small familiar things given Debian gave birth to Ubuntu.

I've found the stable version to be incredibly stable in the past and the testing release has a bit fresher set of packages if you're willing to a risk of occasional jank. If you willing to work a bit for fresher packages still you can find uptodate debian packages of popular software maintained some else than the Debian folks themselves, I used to use a bleeding edge daily version of Emacs myself and installed Spotify from their own repository.