UX designers mostly make products that have to be suitable for many people. Maybe even for everyone: one-size-fits-all. But not everyone is the same. What if you could put design tools in the hands of the users themselves? With those tools, they can create their own personal products: one-size-fits-one. In this presentation, I will show the developments of our research project in which we are developing a design toolkit that will enable autistic young adults and their caregivers to create technological solutions themselves.