Much like with drugs, the best way to reduce human trafficking and abusive prostitution would be to fully legalize and regulate sex work. In countries where prostitution is accepted and legal, it's safer for both the sex workers and the customers, with less risk of disease and abuse. Sex workers are treated humanely and not condemned. Society in general benefits too, through properly paid taxes, lower crime rates, an…
I've heard that the human trafficking numbers increase with legal prostitution since volume increases also, even if the percentage is lower. The Netherlands has huge problems with drug smuggling and human trafficking despite both being largely legal there. While I don't disagree that prostitution should be legal, it's a bit more complicated than the utopia you just painted.
My remaining question is how we draw the line between voluntary illegal immigration and human trafficking for this class of work. I'd guess from my perspective even the voluntary immigration would seem beyond harrowing and carries risk of abuse and death along the way, so it would be easy to paint all of it as bad, yet clearly many think this is the best chance for them and their families.