Just have a seat on a stool beside a mirror. It depends how long you want it to be though. The best would be to make it so you can have one height one way and then flip it on its side to go lower/higher. That way you could have a low/high box in one. I'd say 10-12" would be a pretty low box. 10" for me would be around where I free squat to maybe a little higher.

You could do like a 10" x 14" box. That would probably be slightly above paralell and slightly below paralell.

Lol don't listen to me, depends how tall you are.

IronWorker