How to get mbed os to enter sleep mode in the absence of RTOS not being included in mbed os 5.15.x

I have an application compiled for the NRF52840 _DK and in order to reduce the size of the application I have removed the RTOS from being compiled and also I use the Nano library to further reduce the size of the application firmware. However now that I have achieved the right reduction in size, I am not sure what is the best way to get the device to enter Sleep mode? As it is usually the RTOS Idle thread, that would handle the device entering Sleep mode. How would I achieve the same in the absence of RTOS?

I have asked this question previously and I was told that in the main loop when I determine there is nothing to do I could call the Sleep API, however how do I manage this when using mbed Event queues, since its managing the main loop in my case, which is invoked in Dispatch Forever mode? There is no method in the Event Queue to determine there is nothing in the queue left to process.