MOSFET High Side Switch of high DC voltage (60V), improvement and advice
You need to back up your thinking about five steps. It should not be

I need to cut off the input to a regulator, so
I need a high-side switch, so
I need to convert from a low-side switch

Instead, it should be

I need to disable a regulator, so
I need a regulator with an enable line.

The simplest case is something like a ZXTR1005K4 with 100Vdc in max, 5Vdc out fixed, and your pushbutton going to the enable line. This doesn't take into account that - if I were to make a highly dubious guess that your regulator input current is 60V/400R = 150mA, this would exceed the current rating of this device and you'd have to shop around a little more.
The even simpler thing to do is revise your idea that it's hard to get a 60V-capable pushbutton, and simply put it in the input path of a fixed regulator with no enable. There are many off-mom switches that satisfy your criteria.