Yes, maybe body separator would be a better term. Maybe there are better names for that, I don't know. Not my native language...
It should be rigid and the area touching the body should not me too small. Ideally adjustable in distance, but you will find this only on some expensive models.
With neck stop I mean the point where the neck gets bigger (on an acoustic double bass this is the point where the neck is mounted on the body), so the thump stops there if you glide up. This is usually the fifth, sometimes a minor sixth of the empty string, but never anything else on a double bass.
You have no frets, so this is the major orientation point for any double bass player. You cannot look on markers (at least you should not for many reasons).
You can put some wood of the back on the neck for tactile feedback at the right position, but it would be a lot of work getting the curvature to avoid damage to the neck.
For a fretless BG player it might work, but still needs some more time to accomodate.
Some db players also want a left upper edge of the body as simulation of the top plate for going into thump position, other are happy not to deal with it, YMMV.