Due to their small surfaces, wearable devices make existing techniques for touch input very challenging. This paper proposes deformation input on a tiny and soft surface as an input modality for wearable computing devices. We introduce DeformWear, tiny wearable devices that leverage single-point deformation input on various body locations. Despite the small input surface, DeformWear enables expressive and precise input using high-resolution pressure, shear, and pinch deformations. We present a first set of interaction techniques for tiny deformation-sensitive wearable devices. They enable fluid interaction in a large input space by combining multiple dimensions of deformation. We demonstrate their use in seven application examples, showing DeformWear as a standalone input device and as a companion device for smartwatches, head-mounted displays, or headphones. Results from a user study demonstrate that these tiny devices allow for precise and expressive interactions on many body locations, in standing and walking conditions.