Tall or Standard Chair

I am taking a deep breath and I'm about to order a Gokhale chair.  I'm wondering about which. height to purchase.   I am 5'7 or 5'8.  When I measure the height of the chair I think I need, it's about 20".   But that could change depending on the height of a new computer or perhaps other factors.   I'm wondering if perhaps I would be better off getting the tall chair.   If it turns out the standard size is too low, I don't know what I would do.  It the tall chair is too high, then I could put some realms of paper under my computer so that it is also higher.  Does anyone have recommendations?

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