Shallow DOF headshots

I work on a ship. It's not a cruise ship. I have a "studio" on board and the light is an awful combination of fluorescent, halogen, and tungsten. I've created modifiers using velum-like paper and my backdrop is a patterned tablecloth.
Due to the low light and the vessel's constant motion I end up shooting with a shallow depth of field most of the time. Here are some of my recent headshot attempts; edited in Lightroom only.
Canon 6D, Tamron 70-200 SP VC 2.8