Don't really know about the HDMI cec, but I use one of these remotes which works perfectly with Kodi (it seems to just work like a wireless keyboard that just sends keypresses for shortcut characters corresponding to the function of each button, and those shortcuts are some kind of standard that Kodi supports, so this kind of remote - that also works for Android stuff - works fine with Kodi).

The only quirk it has versus the remotes that come in commercial solutions is that whilst the Power button in the remote will switch the Mini-PC OFF, it won't switch it back ON (for the obvious reason that it uses a USB dongle and the PC when switched OFF won't recognize input from the dongle).

I first got one which had even more buttons (also working fine with Kodi), but the remote's build quality was shit and it didn't took long for some of the button on that one to stop working reliably.

This one has been working fine for about a year now.

I do have a keyboard and mouse attached to that Mini-PC because it doubles up as home server and once in a while I have to do something on it which is more easilly done directly there with a UI rather than remotelly on the command line via SSH (or I simply don't want to boot my main PC to access the Mini-PC remotelly), but to just consume media via Kodi nothing else beyond that remote is needed.