Sometimes selecting a text that contradicts your other texts, or agrees but from a different angle, can work wonders.
Speaking from my own experience (forgive the longwindedness): for my dissertation I looked at how the authors explored the necessity of a balanced society around us for the maintenance of decent behaviour. Not exactly a purely original topic, but I tried to look at it in a new way by making "balanced" the key word - I used Heart of Darkness and Lord of the Flies as standard texts for that topic, but then selected 1984 as my third text. I argued that 1984 essentially makes the same point, but from the opposite direction - while the first two texts show how removing civilised society leads to a degradation in decency of behaviour, 1984 shows that by increasing the strictness of social boundaries the same effect can occur (Winston's rebellion, gross by his own society's judgement, as well as the behaviour of the Proles, basically - I won't prattle on too long). Therefore, a balance between an anarchistic lack of social boundaries and a totalitarian excess of social boundaries both lead to a disintegration of our basic moral decency.
In a similar way, I think you could do something like The Handmaid's Tale with "loss of childhood innocence". You could look at how the "loss of childhood innocence" is often incomplete, and while we view the more cynical approach we take as adults as somehow sullied in comparison to that innocence, in reality we are still so very innocent and ignorant, taking so much for granted. That's a key theme in The Handmaid's Tale. I'm just spitballing here, but you see what I mean - your three texts can actually sort of disagree, as long as you can craft a strong argument out of them, and it gives it a much more original flavour.