As smart textiles are becoming more present in our lives, investigating and designing textile interfaces has started getting more and more attention. Still, very little research has been done on how to design interactive elements for non-wearable textile interfaces for the best recognition, perception, and interaction. In this paper, we present initial assumptions for designing such interfaces, which we derived from working intensively with our partners from the industry. These have been further explored with experts from the field during interviews, and finally tested in a user study. As a conclusion of the study, we define five design recommendations for textile interfaces and present several prototypes that demonstrate them in practice. Our recommendations cover tactile contrast between textures, heights, and shapes; minimal recognizable size of elements; perception of concave and convex shapes as interactive elements; indication of interaction through shape; and recognition of tactile symbols.