My 2-cents, after 43-years at fretless bass.
In late 77, beneath a full moon, I pulled the frets from my only bass at the time, a 66-P-bass. ... What an eye opener that was. ... One thing I realized is, I had to get my left hand finger positioning together and fast. ... After, I did, I removed that from the equation because, this was a time we were playing 4-hours a night, 6-days a week, running around the stage in a fast paced band. ... Plus, I sang. ... On stage, all I needed was a quick visual point, when I heard my tuning was out then, I trusted my hand position. ... Having the trust in yourself not to have to stare at your hand all the time you're playing fretless takes a long time, no short cuts, so, keep practicing.