I have a Stokke Balans chair (e.g. http://www.ergodepot.com/Variable_balans_by_Varier_p/v100.ht...) which works really nicely to align your spine and allow you to move around. Unfortunately the pressure on your shins becomes uncomfortable after a while, and if your back muscles are weak it takes a while to be able to use it for a while without fatigue.
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I have a Stokke Balans chair (e.g. http://www.ergodepot.com/Variable_balans_by_Varier_p/v100.ht...) which works really nicely to align your spine and allow you to move around. Unfortunately the pressure on your shins becomes uncomfortable after a while, and if your back muscles are weak it takes a while to be able to use it for a while without fatigue.