One member asked about TRQ sometime ago. Haven't heard anything about them since though. These would seem to meet your needs.
https://www.xbimmers.com/forums/show....php?t=2044456
I'm not sure what would be involved in a conversion from air to coils, but airbags from Arnott and Sachs rears are relatively inexpensive to keep air ride. Plus they're simple to replace ��