I recently had to start using reading glasses. I have, however, broken countless of them. I came up with this open case so that you can keep them in your pocket without breaking them. Use the clip at the edge of the pocket so that it stays at the top. It is optimized for ease and speed of use, you don't have to take it out of the pocket.

For strength I recommend PETG. If you place the model upside down, no support is needed.

For remixing and resizing, go to the Onshape document. It is built parametrically so it should be easy to change the dimensions. Copy the document and change the values in the first two sketches.