+1 for GHS Brite Flats.

I use monel flatwound bass guitar strings by
RotoSound. Seems to be some GRRR in them but then
again that is mostly from technique.
I was using Dean Markley Blue Steels but stopped
due to the fretboard being chewed up by roundwound strings.
 
slawie

I absolutely love DR Sunbeams on my David King fretless 5. Really good growl and every other tone I can imagine out of that bass.
 
As much as I like flats, I'm not a fan for fretless.
 
YMMV, LOL, etc.

Wishbass and Alembic, the polar opposites in the world of custom basses, but both awesome, in their own fashion.
 
My experience/understanding of the halfwounds is that they are intended to sound like rounds, but feel like flats. I really like the D'Addario halfwounds

I use D'Addario half rounds for all of my fretless basses and some fretted basses.  I have lost some high frequency hearing due to tinnitus and I need the boost.  Plus, flatwounds are like pluckng telephone poles!

tubeperson - clearly you haven't tried Tomastik-Infeld Jazz Flats, they're very supple.