Your operating system such as Windows or Mac OS X should be able to remap the input of the keyboard to Dvorak, Colmak, or other national language layouts. You should not need any support for this from the keyboard hardware.
By the way, transitioning to a standing desk may help with your back and slumping. Working with a good Pilates trainer helped me immensely.
As for ergonomic keyboards, consider various products from Kinesis. My favorite is the Freestyle2.
Kinesis offers a Bluetooth version, the Freestyle2 Blue (one for PC, one for Mac). Supports switching between up to 3 computers/devices.
The Spring of 2016 may bring an innovative keyboard being developed as a Kickstarter project. See Keyboard.io. You can read all about this team’s development adventure.
Yes, that is wood, real solid wood. The “butterfly” shape was discovered by accident to be comfortable.
The Keyboard.io is entirely open-source, both the hardware and software. Built on top of the open Aduino platform. It can be completely re-programmed by you or third-parties. No restrictive license. You can even program control of each key’s individual LED light.
For the convenience of non-programmers, a simple utility app arbitrarily re-assign keys any way you desire. They even build in an extra physical key with no assigned behavior, for you to dream up an assignment.