If you use a small, portable device such as a netbook, then Plasma Netbook is the KDE Workspace for you as it was built specifically for those kinds of devices.
You can install the
kde-plasma-netbook package to get only the workspace and basic applications. There's also a
kubuntu-netbook package but it has a dependency on
kubuntu-desktop, so it installs a lot more (you get Netbook and Desktop workspaces.)
By default you'll get KDE 4.8.x. If you want 4.9.x then you'll have to add the Backports PPA, as mentioned in How do I install/upgrade to KDE 4.9?. As it's also mentioned there, it's a backports repo and it might give you some problems. I have updated to 4.9 (currently 4.9.3) without a single problem, but I use Kubuntu, i.e. no Unity here (although I do have XFCE installed also).
If you really want to try it without having the risk of messing up your system, there's the virtual machine route, like Virtual Box.