This base is way better than the original one that comes with your chair! Should be included right off the bat. But definitely well worth it!!!
I originally had a plastic base. After a little over a year two wheels broke off in the exact same form suggesting a weak point in the mould. Replaced it with the metal frame and it has worked well so far. It sits a bit bigger than the original base but I felt that one was a bit low so no harm done. I have only had it for a couple weeks but I assume it will hold well.
Techni Metal Base
the only thing I don't like is the hydraulic doesn't go down far enough.