In any case, make sure the intonation is correct on whatever you buy.
Totally agree with this one. My first fretless was a $300 used MIM jazz w/ lines. The neck and intonation were way off. It made it very difficult to play chords. And to get the correct Mwwwwawah sound, the neck needs a slight bow - not flat.
My second fretless - yes I like the first one that much - is an Alembic Elan w/o the lines on the fingerboard. It does have dots on the side at 3, 5, 7, 9, 12 ..... I only occasionally glance over when playing. Because we constantly change the songs we play at church, I'm looking at the music too much. This bass also needed adjustments - partially due to different strings. Also because I don't think it was played that much. One bridge piece was moved about 3/16-in to get the intonation right. Now it sounds awesome.
Now you have to figure what strings to get. I tried flats, half-wounds, and round-wounds. I much prefer the round-wounds. I really like the DR Highbeams in regular light gage.
Look up Gary Wills set up guide on You Tube. It's a great video that helps get the bass set up properly.
ENJOY!!! and welcome to the wonderful world of Fretless Bass!!!

Steve
PS - you're going to be amazed at how many people never heard of a fretless bass.