I had the privilege, at the end of 2016, to spend time with Elly Stone in New York. We often sat at her kitchen table over breakfast or an evening snack, and we talked about acting and singing, and acting technique and she shared with me some memories of acting classes, in particular, with Stella Adler.
We commiserated over the lack of good voices, good diction, in young actors. One morning she showed me how to position my torso so that there would be an available endless breath, without tension, that would support my voice indefinitely. She acknowledged that the Alexander technique was useful, but that Feldenkreis was far more useful because of its attention to the pelvis, and that it's from the pelvic area of our bodies that the breath must come. She said, "Voice, in its natural state, is fueled by your breath and if your posture is correctly aligned, your breath will be drawn from a repository that never becomes empty."
She suggested I listen to Burt Lahr in the recording of Waiting for Godot (on YouTube). I suggest you do the same, and listen to her singing Marieke from Jacques Brel is Alive and Well and Living in Paris.