I have never given a blow job, so any advice from me is suspect.
However, I have studiedsome of the biomechanical aspects of it from an observers pespective.
I think kappakittycat has a good point. Sitting on the edge of anything is a good idea.
Also, remember
you can shift the stick.
Its not a joystic
but it is flexible. Its like a hinge it moves down and up but not well side to side, so don't be afraid to keep it in a comfortable position for yourself.
On a lighter note, if you bought an elastic band, like a yoga band, you could attach it to something and use it as aforehead rest to provide support for your nneck as you are bobbing up and down . . .