This can be really cheap and simple - I purchased a generic USB foot-switch a few years back. Just search eBay and you’ll find loads of them - some with just one switch, and some with 2,3 or more - I can see loads there now for about £15.
These devices come with piece of driver software and a control panel that allows you to assign the key-stroke of your choice to each switch. For live ‘stop/start’ function, just assign ‘space bar’ and off you go. Clearly this method connects to your computer rather than to the MIDI port on your keyboard.
In the studio it’s a great way to get the benefit of needing to use the mouse and keyboard less - especially if you are musician that’s recording yourself, and you need two or more pairs of hands. Your feet start to become part of your controls…keyboard players and pedal steel players, and guitarists with effects pedals will know all about this.