I thought of you when I read this:- https://z4-forum.com/forum/viewtopic.php?f=7&t=118657
The ZHP is noticeably heavier than what BMW fit, and is a big improvement.
Or you could buy a new one:- https://www.ebay.co.uk/itm/Genuine-BMW-6-Speed-M-Leather-Gear-Knob-ZHP-330i-E46-E60-E61-E63-E64-F25-F26-/122919443539
But you may get one a bit cheaper from either Soper of Lincoln or Cotswold BMW if you quote the OE Part Number from the ebay advert, as they give a forum discount.