I've heard a quite bit about the seatbelts in the Z4 rubbing into your neck whilst driving. I'm 6'2", so my seats are as low as they'll get, and I had the same common issue.
However, there seems to be all kinds of odd solutions suggested, such as additional sections of belts, or clips used to hold the belt away from your neck?
I simply got these.......Soft wool finish and amazingly comfortable
https://www.ebay.co.uk/itm/403719165546
Easy