Introducing DeformIO, a novel deformable display with co-located force input and variable stiffness output. Unlike prior work, our approach does not require pin arrays or re-configurable panels. Instead, we leveraged pneumatics and resistive sensing to enable force detection and stiffness control on a soft continuous surface. This allows users to perceive rich tactile feedback on a soft surface and replicates the benefits of fluid finger movement from traditional glass-based screens. Using a robotic arm, we conducted a series of evaluations with 3,267 trials to quantify the performance of touch and force input, as well as stiffness output. Additionally, our study confirmed users’ ability to apply multiple force inputs simultaneously and distinguish stiffness levels. We illustrate how DeformIO enhances interaction through a vision for everyday interaction and include two implemented self-contained demonstrations.