This is an improved design from Alan Ball that uses the morphing struts to correct for seat tilt as you morph up and down.
Close-up of the seat adjustment mechansim showing the base supports for a slung seat design. The link arm shown in red causes the seat to adjust as the morphing happens.
The next step is to build a test rig to see how all of these designs work in real life before committing them to a finished design.
Here is the e-Drawings file for the SolidWorks model: You'll need the free e-Drawings Viewer (for Mac or PC)