What fabric do you want on the chair? (most important thing on all chairs)
Poly is cheap and durable however sitting on it for long periods of time means it wont breath as much
Wool is probably the best, breaths nicely, durable and is by far the best for comfort,
Vinyl or leatherette's look the best are okay on the durable side however wont breath if you are sitting on it for long periods of time,
The more expensive the better, i always look for chairs that are 5-8 hours recommended sitting times, even if you are sitting on them for 1-2 hours the custom positioning you can do with the chairs can make an amazing difference
Officemax are always a good place to go to, good fabric and good variety Dawell (however they may not sell straight to you but may put you onto the retailer)
Thats all the places i can think of in Wellington atm
We specialise in ex-corp office furniture so quite often get chairs by herman miller etc. At the moment we have a bunch of Formway Life Chairs which have all be commercially cleaned and serviced. I suggest looking secondhand as you will get an excellent quality product without having to pay full price and these chairs are designed to last a lifetime..