The confinement of light to material interfaces and thin layers, i.e., the propagation of surface waves along metal-dielectric interfaces or guided waves along dielectric waveguides, enables a multitude of photonic applications in (bio)sensing, optical circuitry and optical actuation. Several research groups try to enhance our control on the propagation of confined light by making use of artificial materials, e.g., metamaterials with tailored optical properties determined by subwavelength structures. To efficiently determine the appropriate geometry, spacing and composition of metamaterial building blocks, one often relies on a geometrical design tool known as transformation optics. Transformation optics determines the specific metamaterial properties that impose desired light flows inside a metamaterial device―based on coordinate deformations of initially straight trajectories―leading to extraordinary applications such as invisibility cloaks, optimized Cherenkov detectors and efficient beam steering devices. Unfortunately, the conventional application of transformation optics to slab waveguides leads to impractical and bulky designs, implementing metamaterials both inside and outside of the waveguide’s core. In this contribution, we restore the two-dimensional nature of guided modes by introducing new relations between two-dimensional coordinate deformations of confined light flows and the waveguide’s properties. In particular, our designs consist of metamaterial waveguide cores of varying thickness without need for metamaterials outside of the core. We verify the effectiveness and versatility of our design with three proof-of-concept devices: a beam bender, a beam splitter and a conformal lens. We anticipate that the seamless design of multifunctional metamaterial waveguides, combining benders, splitters and lenses with one consistent coordinate transformation, opens up new opportunities for guiding confined light along optical chips.