How to put an MCU to sleep when operating from an SMPS?

I have a device running on a 9V battery. There is a simple buck switcher to drop the voltage to 5V (I need the switching regulator to save on battery life). There is an MCU in the circuit and when I press a momentary button it will be detected and the device would go into sleep. The problem is I would also need to stop the SMPS from running as it will draw current even with a very small load. The SMPS has an enable pin which is active low so I need to pull it high in order to shut in down. The problem is that if I shut it down I don't have 5V to wake up the device from sleep.

So I need a way to use the momentary switch to put the MCU to sleep and shut down the SMPS and when waking up I need to turn on the SMPS and it wake up the MCU. I guess some solution with MOSFET switches maybe? If anyone can help it will be appreciated, I am sure there is a "standard" scheme for this.