Nimitta

Buddhadasa talks about nimitta, a pleasing and calming image, in the context of calming the breath. 

In metta, one of my goto images is children sledding, because I loved sledding as a little kid. 

It's also an option to visualize a sadhana during the anapanasati if that is supportive. 

Green Tara is popping up my visualizations. My sadhana is Green Tara, and some of the items in the visualization is the crown of the colors of the 5 jinas. It starts out with a lotus moon mat, out of the void. Tara was born out of a lake of tears, seeing the world's cries. There are also parallels with the 5 elements. She holds a lotus that blooms next to her right ear (source). 

You can chant the Green Tara mantra: Om Tare Tuttare Ture Svaha.

Her right foot is extended to step off the mediation pad, to launch into action.

Sartre was a philosopher but he was also active during the resistance when Germany occupied France. I honestly don't know what he did besides join a writers resistance group. I'm reading Sarah Bakewell's fun book on existentialism.

Sartre also emphasized freedom, a theme in Buddhism.