Object outline component

I would like to create a script that attached to any 3d game object creates an outline (silhouette effect) around it when certain bool in the script is set to true. This would be used to create a highlight objects when selected with mouse.

I found many shaders on the internet (which seem to work, but the outline produced by them is kind of inconsistent), but it doesn't help, because my 3d objects are already textured, have submeshes and some of them have complicated materials (all of them use Unity Standard Shader but some of them have a lot of options) and changing shader in one of the materials creates a mess. The same applies to just adding another material to material array of an object.

Should I copy Unity Standard Shader and modify it to draw outline and swap it in material at runtime if I want to save all of the material's settings? Is there a simpler way? No, I don't own Unity Pro.