Hi - can you pls clarify what you mean by "Make sure all four sides of the bassinet are at least 300mm higher than the top of the mattress base to stop baby falling out." Is this 300 mm from the bottom of the mattress or the top of the mattress? This is related to bassinets: https://rednose.org.au/article/bassinets
Red Nose Education
It is related to the top of the mattress, however, the mattress for a bassinet should be no thicker than 75mm.
Product Safety Australia have the full guidelines (buying tips) here: