If sleeping on your back is more uncomfortable, it will help you fall asleep more slowly and lightly. This will help you be more aware until the transition from waking to dreaming for WILDs and more aware during the dream itself for DILDs.

But in order to become lucid during a dream, you also have to remember what you're aware of is a dream. Sleeping on your back won't help you do this.

I for one regularly lucid dream without sleeping on my back.