Height-adjustable supple member

A height-adjustable supple member for lying and/or sitting furniture, comprising:

• one or more adjustable springs, each configured to change in height along a central axis under the effect of a radial stress relative to the central axis, and
• a rotary part including one or more rails each extending over an angular sector about the central axis, in a plane perpendicular to the central axis, from a first end to a second end more distant from the central axis than the first end, each rail cooperating, in the radial direction relative to the central axis, with a corresponding adjustable spring among the one or more adjustable springs, and the rotary part being able to rotate, about the central axis, so as to exert, through each rail, said radial stress on the corresponding adjustable spring, to vary the height of the adjustable springs, wherein in a first rotational position of the rotary part the first end of the rail retains the springs at the hinge at a radial distance (ra) from the central axis Z while in a second rotational position of the rotary part the second end of the rail retains the springs at the hinge at a radial distance (rc) from the central axis Z greater than distance (ra).