Ok so I use a split since two months and the switch is certainly not automatic but the solutions are fairly simple. I’m a good exemple of a user scenario that requires a lot of one-handed operations because I mainly edit text and not writing it and I use a lot of GUI related to graphic work (illustrator mainly but also photoshop). For the following process, I should make clear that I’m on a Mac and it’s clearly a big plus since this platform promotes consistent patterns of shortcuts.

Text edition :

• I have a ⇧ and a ⌘ key on my thumbs and arrows on a layer triggered by a thumb. Lateral arrows are set to trigger ⎇+arrow when long press and ⌘+arrow when double presses. With the ⇧ on the right thumb and the arrows (and the layer switch key) on my left hand. Give it a try, I can really quickly select words, lines, etc. For a quick word selection/replacement I have also a simple macro that trigger : “⎇+⬅️, ⇧+⎇+➡️, ⌘-c” (the copy part is just in case I want this bit of text in my pasteboard.
• I use vim whenever I can. It makes the use of a mouse irrelevant, don’t worry the main selection operation are easy to learn.

GUI

• It’s more tricky but I really advise to take a note of every friction in your workflow and find a solution when mandatory. I could give some of my settings but it’s very specific to the app I use. The only advice that could match any situation is a “esc” signal that is always accessible as a combo with the W+E combination, in every layer, I also have a space and I try to get the maximum access of elementary keys but when it replicates a primary action on my right hand, I hide it on my left hand (combo, double-tap)

I should mention that I use Colemak and that it certainly help compared to layout leaning toward hand switch (Dvorak, Bepo…). But if you’re on QWERTY it should be good.

Yes the staggering of the Cantor is perfect but all the thumb keys are 1u and I’d really want a larger key for the inner one.

It’s exactly what I want : a Corne with a lower pinky column relative to the ring finger. It’s so weird that this design is not yet popularized !