The reasons you and other serial critics of the current government's policies struggle to offer a solution is that you conflate the movement of asylum seekers with broader social objectives.
A simple solution for example is for a deal between Australia and the UNHCR to take responsibility for those on Manus for a number of refugees to be accepted by Australia from the UNHCR. That closes Manus without encouraging the people smuggling trade.
Unfortunately, the UNHCR also seeks broader social objectives in the movement of asylum seekers with the human misery that results from illegal people smuggling an acceptable cost of achieving those objectives.
Who are you kidding? As if you care about the "human misery that results from illegal people smuggling". You care about them not reaching Australia.