I use D'Addario chromes on my fretless StingRay and they are great, but if you want even more zing...
Just before the lockdown I played one of the EBMM BFR StingRay Specials
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and they come from the factory with Cobalt Flats ([Invalid or Expired Link Removed]), which I have to say were something else.
How much of the sound was the strings, how much was the new pickup/electronics and how much was the laquered fingerboard I wouldn't like to say, but the package was incredible - probably the closest to a round sounding flat I've ever played. I've no idea how long they stay sounding good, or if they get better before they get worse, but they might be worth a shot.