First, if one saddle works for you I'd say just use the same saddle on all your bikes.

But I went through all of this, numerous fittings, numerous saddles, etc and never found a saddle that magically made things perfect.

In my experience the root cause of numbness downstairs is poor core strength. You end up putting pressure where it shouldn't be because your core isn't holding you upright. What initially fixed it for me was this workout warmup routine called Limber 11:

For me at least, after I did that for a while I changed to where any decent saddle worked fine.

Core Strength + Biking is annoying - you need core strength to bike well, but biking doesn't build it.