Simple mosfet sound blaster keyer schematic needed

Hi, I have built this power oscillator keyed CW by a mechanical manual key.

I would like to replace this key with an electrinic one, that can be triggered by the sound output of the soundblaster of the PC.

In the past, I did it with this relay-based circuit I attach, but now I seek a more simple way, without the use of a relay and that many components.
I believe that a single power mosfet will be able to do this, since I think that it's gate requires less current to trigger the mosfet? I think it has to be a P-type mosfet since it will be connected on the +V (high side switching).

Can you please suggest such a circuit, having in mind that the transmitter current can be as high at 700mA at 35v (max)?

Maybe a LED/LDR in combination with the mosfet or a "power optocoupler"?



Or a thyristor?



Will such a simple circuit work?
I know it uses a relay and 4 components, not just a single mosfet as asked at first...
In it, how to limit the voltage to the relay to 5v, if the vcc is 30v? use a zener in parallel with the relay?