I'm not sure if you found a solution to this, but I've been using KVMs for almost 15 years now so I thought I could offer some help.
The hardest part of modern KVMs is the V=Video. Luckily, most modern day monitors now have multiple input support, so switching the video right on the monitor itself can solve that issue. Plus, if you're just leaving your Macbook open, you can just use the built-in screen (think multiple monitor setups) unless you really need it on the desktop--then you can just use the input select on the monitor.
So now that video is out of the way, you're left with the easy task of K and M. Almost any cheap old kvm switch will do for just k and m. I actually use a very similar setup to what I'm recommending, having two monitors on two different computers in a multi-monitor setup and just using the k and m part of my kvm to switch the keyboard and mouse. I can see what both systems are doing all the time as I'm not switching video at all.
Hope this helps!
