ZFR: I like my OS not changing and remaining same (except for security updates and the like) for a few years, followed by a complete overhaul, than having tiny changes made to it frequently.
This sounds like Debian stable is what you're looking for, to be honest. Even after new releases, the oldstable branch is generally still supported in some way for a year or two after the new release (and in some cases, even after that). I know earlier in the thread you mentioned having some apprehension about multimedia support, but getting appropriate audio/video libraries, etc, loaded is pretty easy either way, and there's also the deb-multimedia repo if you explicitly want to make things easier.
Others also mentioned KDE Neon which is built upon Ubuntu LTS versions. It's basically
the KDE distro, but you'll be seeing more interface changes more often due to KDE being updated on it constantly vs being stuck at a static version.
EDIT: Or just use Kubuntu LTS, for a more non-changing KDE Ubuntu. It's been a while since I looked into it, but IIRC, you can change a Kubuntu install into KDE Neon later on if for whatever reason you wanted to switch.