Take it to a luthier who knows how to set up a fretless. Pretty much that simple. Even better would be a luthier who takes the time to watch you play a fretless, then asks you your expectations, and preferences. Sets up the bass to your spec, and sends you on your way. From that point it's all about you leaving it alone.
Understand I have been doing this for going on 30 years, and I know how hard it is to find a good setup guy, especially for fretless, and even more how difficult it is for musicians to keep it this way.
Best of luck with this.
