Kaihl choc switches (the V1 type) are going to have the shortest travel out of the keyboard switches that are common enough to use, and that’s what most low-profile hobbyist mechanical boards out there use. There’s a “choc amber” version that recently became available that have the shortest travel distance among choc switches (1mm actuation, 3mm overall), but they’re pricey and I haven’t seen anyone fill a keyboard with them yet. Those are also designed for fight pads, so I don’t think they’re made with silence in mind.

There are “silent” choc switches on their way (developed by Darryl lowprokb.ca), but they’re not available quite yet.

There’s also the Kaihl X switch with a 2mm overall travel distance, but they’re also pricey and I think it next to impossible to get key caps for them (at least it was last time I checked). Hazel is the only person I’ve seen make a keyboard for those: https://github.com/hazels-garage/shortstack. Awesome stuff, but probably not easily obtainable.

Thanks for sharing the layout along with your very nice build. Which physical thumb keys do your have mapped as the two thumb keys in your layout?