This keeps your existing US toggle switch and install an IKEA square Tradfi switch over the top of it. Because this is NOT UL certified, print and use at your own risk. The image shows one printed in ASA. I used tree supports for the backplate which is why it looks so rough.

I provided two versions. The tradfi-switch version is the one pictured in the photo. The tradfi-switch-round version is a bit more artsy for those that want something a little different.
The indentations on the model are for 8x3 magnets (like these). You really only need the one in the middle. They friction fit in - but you could also put a dab of superglue in to make sure they stay.
I recorded a short video so you can see it all around:
When I printed this, I used the following settings:
You could probably use more defaults, but this is what I did.
Print it and glue the magnet(s) in.
The author marked this model as their own original creation.