Check the Jerzy Drozd series. Very exotic basses from Spain (If I'm not wrong, Barcelona). They offer a wide range of models. Seriously considering to order one of these.
Never thought .175 F# would articulate that well on fretless. But it seems more bassists like the idea to add sub-contra in their sound. Don't have any experience with fretless basses, still using roundwounds.
Like very much what Thesseling is doing here and never heard somebody before picking up such influences with electric bass. Of course it's not music meant for everybody. At least he has the guts to do something very different with his instrument and collaborates with several contemporary...
Exactly, you need a reference. A matter of calculating, then playing to see which gauges feel comfortable and sound good enough (perhaps which do not).