I made this in Fusion 360.

It is a 25mm sphere with a right angle cutout so you can fit it over corners.

It should be scalable. 

To print it, rotate it so the opening faces downwards and all 3 points touch the bottom of the build plate in your slicer. then pull it downwards so the first layer area gets a little bigger. just use a brim like in the picture and you will not need support.

I use it to protect my son's head sharp corners of our coffe table.