At most you can customise a chair bought at a furniture store with a throw pillow or a blanket. But Keren Shiker's wonderful Sink In seat actually starts off as a large bundle of foam pieces that have to be slid around before you can comfortably sit.
It's not unlike those pinart toys that use tiny metal rods to recreate the shape of your hand or face. But on the Sink In those rods are made from squishy pieces of foam held together with a pair of adjustable wooden frames. As you move the pieces of foam forward and back, eventually you can create a comfortable place to sit that's customised for however tall or large you might be.
And while the Sink In might look like just a concept or a design exercise, the chair is actually available for sale on Shiker's website. It's $US700 plus $US80 shipping, but it's also guaranteed to fit you perfectly because you can just keep readjusting it until it is.