Last week I bought a new footswitch at a nearby music store. It's a Roland DP-2 Momentary footswitch, normally used for keyboards.

The guy in the store told me that the footswitch will "close" when pressed. But it was just the other way around.
So I had to take my soldering iron to change connections on the internal switch. A few minutes later it worked as a proper Push To Talk footswitch. And that for only 13 euro.....

In combination with my Heil Pro 5 Headset it works great.
No unwanted transmissions as I sometimes had when operating on VOX mode with background sounds I produce sometimes.

It took a few minutes to get used to pushing the switch with my foot at the right moment when I wanted to talk on the air. But after that learning period I don't want anything else when using my headset.