The Microsoft keyboard is good (their best yet, I think), but only Space and the two Alt keys can be pressed with the thumb.
On my keyboard², I have Alt, Backspace, Ctrl, and "Fn" for my left thumb, and "Fn", Enter/Ctrl¹, Space, Alt with my right thumb. Slightly less comfortably, I also have Esc (left) and Delete (right).
The Kinesis Advantage 2³ is the most common mass-produced keyboard with thumb keys like this.
¹ It's enter if I tap it, and Ctrl if I press it in combination with another key
The Microsoft keyboard is good (their best yet, I think), but only Space and the two Alt keys can be pressed with the thumb.
On my keyboard², I have Alt, Backspace, Ctrl, and "Fn" for my left thumb, and "Fn", Enter/Ctrl¹, Space, Alt with my right thumb. Slightly less comfortably, I also have Esc (left) and Delete (right).
The Kinesis Advantage 2³ is the most common mass-produced keyboard with thumb keys like this.
¹ It's enter if I tap it, and Ctrl if I press it in combination with another key
² http://www.keyboard-layout-editor.com/#/gists/501437fce9123e...
³ https://www.kinesis-ergo.com/shop/advantage2/