If you are willing to try a new keyboard layout Truly Ergonomic makes a mechanical keyboard that is structured oddly. It is suppose to be better for you than the standard keyboards (during long term use) and they have different key switch options. It should also be noted that this keyboard does not have a keypad, if you find yourself using the keypad a lot then it may not be a good choice. (Personally I did away with my keypad years ago, never used it in my development work and wasted desktop space).
Switch (key) types:
These switches are quiet and provide a gentle tactile feedback
that helps you feel when each key registers, allowing you to use minimal force.
These switches provide a light‑click‑sound feedback and a
gentle tactile feedback that helps you feel and hear when each key registers.
These switches are quiet and provide a firm tactile feedback
that helps you feel when each key registers. If you have used Soft Tactile mechanical switches and find them too soft, these switches would be best.
On membrane keyboards, the key passes through a plastic layer with electrical contacts and then through a hole to a second layer that interrupts a circuit to register the stroke. Pressing through these layers makes typing on a membrane feel like tapping your fingers on old, stale Jell-O.
(Membrane is standard keyboard feel and the quote is a bit exaggerated but does explain it well. These keys are soft and have not tactical feedback.)
Note: There lots of different types I have listed some of the common types. Also if you are thinking about a mechanical keyboard please remember your coworkers and that typing can be quite loud with some switches (notably the click ones). Maybe ask them first if they are ok with a noisy keyboard.