Phone Herman Miller, ask them where the nearest local dealer is that can give you a test drive.
Phone the dealer and ask to try out the Aeron, Mirra 2, Embody, Cosm, Sayl.. etc.
After a long time of mulling over the Aeron or Mirra 2 from previous, separate visits to JL, I decided to finalise it once and for all with a side-by-side test.
Tried all of the above bar one:
Didn't find anything amazing about the Aeron or Cosm, and simply couldn't justify a purchase based on price vs comfort.
Mirra 2 arms killed the deal for me.
They didn't have an Embody in stock but I was only interested in seeing what the Logitech fanboys were getting.
I had tried a Sayl in the past and really liked it but did not take it seriously as a choice. Amongst all of the above, it was comfy and functional enough for the price to seal the deal. £360 brand new.
It's a lot of money to spend on a piece of office equipment. It should be verified and not purchased based on word of mouth.