Using a transistor to control amplifier

Hi everyone, I’m building a Volumio/PiZero/pHAT DAC player inside an old radio for my sister. I setup the basic electronics yesterday and everything works pretty well. However, since the amplifier is on a different power supply than the RPi (as recommended by the manufacturer) I get a lot of static coming through the speakers unless the Pi is on.

I plan on adding an on/off power switch to the amplifier, however I think it would be a good idea to run a trigger from a GPIO to a transistor that then enables the amplifier by closing the circuit in it’s power line (5V). The software side is easy, just run a simple RPi.GPIO script on startup that pulls a pin high. However I’m pretty new at electronics and need a little help selecting the right transistor.

I currently have a few BC547 lying around, but I understand that their max current is only 100mA, which is not nearly enough. As I understand it, I would need a transistor that allows up to 2 or 3 Amp, and with an amplification factor that is sufficient so that the current draw on the GPIO is well below 20mA.

So are my assumptions correct? If anyone knows any models that fall under this specs that would be great as well, cheers!