Deep breathing exercises work well for me, and I can do them anywhere and any time.
I slowly inhale through my nose for a count of 7.
I then hold it (my breath) for a count of 5.
Then I slowly exhale through my mouth for a count of 7.
I repeat it anywhere from 3 to 7 times until I feel a sort of peaceful relaxation come over me.
I can most certainly empathize with you as those of us who struggle with C-PTSD have so much more to overcome. I once commented to one of my doctors that I was beyond "learned helplessness", I had a bad case of "learned hopelessness".
It does feel hopeless, and so overwhelmingly so at times that I feel as if I'm going to simply float off the face of the earth and out into absolute nothingness.
Those who didn't experience years of abject physical, emotional & sexual abuse starting from an early age (3 years of age for me) can never understand the extra set of challenges it presents to us and our healing processes.
So don't let anyone's lack of empathy or compassion disturb you ... It's a long, painful, tough slog they probably wouldn't even have the strength to endure ... You'll eventually find what works best for you, and when you do, you will also experience some of the peaceful relaxation that I mentioned above.
ps. I also found art & play therapy helpful, as well as writing poems & songs & such ... And I still buy myself a Hello Kitty coloring book and some crayons now and again and allow my inner child to have at it!