Stabilize Upper Body / Constrain certain Body Parts make them not influened by other Animation

I have tried (and sadly failed) to edit animations in a way that makes the upper body stable.

My Character is in first person but I'd like to give it full awareness (see Outlast, Amnesia The Bunker) and i need to have the upper half of the Body be stable but of course every animation e.g. a walk cycle makes the body transform go up and down, shake etc.

Is there a way to retain the animations but make the upper body (chest + head) stable, even though the other parts move?

The Problem is that the body moves in unwanted ways, when i correct the Animation, walking makes the chest and head turn left and right, when walking is not in a fixed height the body (and head) moves up and down etc.

Maybe there is a constrain that makes it possible to only make the pelvis move to a certain height or keep the chest from rotating with the arm motion.

Best regards