@jazmo1999, there’s discussion about this in another thread on these Forums (“The PICK thread”), and elsewhere. 
The general rule for a starting point is to adjust your strap so that your bass is at the same height whether you are sitting or standing. This is what I have always done and is what works for me, but everyone is different.
I can understand your dilemma about comfort vs visual sight-lines, though; I personally would consider comfort to be more important, especially if you will be playing for extended periods. Also, the longer you play and practice, the less necessary it will be to see the fretboard.
HTH and cheers, Joe