I used the Postage Board Mini, which is a controller I designed for hand-wired keyboards. (shameless plug: I'm running a GB for it right now, only 1 day left).
I've been trying to make thinner hand-wired keyboards for a while, and this is the thinnest I've done yet. Next time, I might try making a cutout for the USB-C connector on the bottom plate, so that I can maybe achieve 6.5mm or 7mm. Might require trimming the pins on the switches a bit. If I go lower, I might also need to cover the bottom plate in something insulating (steel plate), I fear that static-shock might be an issue with clearance that close.
I just need to get some proper keycaps now. I need to find something with a Mac OS command-key, as I'm using this keyboard at work, and we use Macs at work.