I saw this question yesterday, just as I was hunched over my Cintiq and working on a page of my comic. Honestly, I don't think my back has suffered nearly as much as it really should have, but I may just have low expectations for how my body is supposed to feel at 31. That said, there are certain things I've done for the purposes of ergonomics that some people feel to be excessive. Not for my back so much, but more for my legs. I installed a custom keyboard tray which has an adjustable height, and sneaks in under my cintiq. The cintiq itself hangs over the edge of the desk, putting it at a relatively comfortable height for use, while still letting my type (though I can't really see the keyboard that easily). This saves me from having to sit too high, and have my legs dangle. When I was working in-office before, I wasn't able to create a setup this... unique, which made things difficult. At one point, adjusting my setup caused me to put immense strain on my legs without realizing it. Then I walked home for the evening, and by the time I got to my apartment, I couldn't walk a few feet without limping terribly. Long story short - invest in your ergonomics, find what works for you, and listen to your body.

If I'm designing for client work, I always do some writing/listmaking first. Almost verbatim to the way it is outlined here in the livestream and more accurately in the Monster Lab course.