Custom Foam Seats
Recently, we had a lot of snow over here, and after some sledging and snowball-fighting, we all sank back-first into a huge pile of fluffy snow. Sitting there was just incredibly comfortable - the snow compressed and adapted just perfectly to the back and the spine. I could have sat there for hours (except for the cold).
This also reminded me of the way they make shoe lifts these days - you just step bare-footed into a box of soft foam, and a week later you have shoes that exactly fit your feet.
Add 1+1 and you start wondering why this system doesn't exist for furniture, in particular armchairs and couches. Just have them take a model of your stature, and get a perfectly comfortable armchair that is designed to fit YOU!
Reward: An armchair that fits me like a glove.