Why not use a relay? Less to worry about for a side project like that. If you don't need sub-millisecond switching then you gain complete isolation, constant voltage output, and AC or DC switching
(you need to stick a transistor between the 555 and the relay anyway so you might as well just use a MOSFET)
Good tip: measure voltage between the output pin and gnd or Vcc in both states and then have a think.
Plus when you're not an idiot like I was, a MOSFET is cheaper.
I sometimes overestimate the ability of the average electronics hobbyist to properly understand a datasheet.