You might find this a funny answer But seriously.
Get a good seating position. (not an expensive chair)
Most important in the whole ergonomics of a desk job is regular movement(don't be a zombie but change your position)
For the rest, all ergonomics are standard things that have been said before everywhere. And pretty much everybody knows in the back of their head. And just listen to your body.
And about the mouse ;)
Just go somewhere and hold them, the one that fits is probably the best for you.
If however your asking this because something hurts in your body. Don't get a left or right handed mouse but get one you can use with both hands and change mouse hand for a while. This also helps sitting more active since you will get annoyed faster ;)
Good luck with your mouse.
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What are your criterias? Why do you need "ergonomic" exactly? Without more details, all I can say is that this question is a duplicate of this one: http://superuser.com/questions/2198/mouse-recommendation
– Gnoupi – 2010-05-25T18:12:22.240