These are two great texts to compare and contrast based on the theme of loneliness. Both texts present us with figures who are desperately lonely and struggling to find purpose in their lives. Note how Eleanor Rigby and Father Mackenzie are presented as isolated, failed and purposeless individuals. No one listens to Father Mackenzie's sermons, and although Eleanor Rigby has a "face in a jar by the door" the song haunts us with the question "Who is it for?" Eleanor Rigby ends up dying unknown and unlamented, and Father Mackenzie ends having to face the fact that "no-one was saved" through his work.
Similarly, the characters in Of Mice and Men are desperate to try and stave off loneliness as best they can. There is something pathetic in the way that Candy is so ready to cling on to the dream of George and Lennie, and likewise Curley's Wife is so hungry for human warmth that she even endangers herself by going to Lennie to find companionship. Therefore a thesis statement that you could use to compare these texts would be:
Of Mice and Men and "Eleanor Rigby" present us with a series of figures who struggle with loneliness.
This would allow you to explore the various presentations of loneliness and lack of significance in these two texts. Good luck! This is an interesting question to consider.