My solution to avoiding back pains is to have a very simple chair at my desk that is deliberately uncomfortable. So you need to try to find new sitting positions all the time. And I work quite a lot sitting on a bit cushion from Muji with the laptop on my knees. again, not very comfortable in the long run but that makes me move around. That seems to be the only way to avoid damage to your body. All those expensing ergonomic chairs and gear make you sit/hold in *the* perfect position. But that position is unhealthy after 30 min too. But there is no way to change/move.
In the iMac I use a tiny Microsoft mouse (I like its wheel better than the one from Logitec (to loud)). On the laptop I love the trackpad. It can be very precise and the hand are much closer to the keyboard.