I 'm mainly a fretted bass player, but do play fretless bass on occasion, depending on the type and style of
music I have to perform.
My first fretless bass was a 1980's Ibanez Musician 4 strng ( they copied the style of an Alembic), it had no lines, but did have dots on the neck under the G string only, I kind of liked this and thought it was a neat idea( they looked like the dots on the side of the neck) I didn't have any problem adjusting from frets to no frets.
I would use a combination of the dots and my ears to play in tune, but relied more so on my ears, also so I don't stare at the neck all the time, which even with frets I have a bad habit of doing.
I had sold that bass last year, along with its fretted brother cause I don't play 4 strng as much anymore, have other nicer instruments and ordered a custom Alembic.
I now use a Pedulla Pentabuzz lined fretless 5 strng, a Zeta crossover upright 4 strng unlined, Guild Ashbory 4 strng lined and a Fodera Monarch Elite fretless 6 string, unlined, but it has fret markers in the side of the neck, they are not very visible.
lines, no lines or side markers........makes no difference its still a fretless bass, in the end its what ever you are comfortable and happy with on your instrument.
its your decision, try as many types of fretless basses as you can.
best wishes,
B.