1) I am interested in how bodily the novel is.
2) I want to look at when ropes are tied around bodies and when bodies are lashed down by ropes.
3) What I am looking into is the troubling idea that survival depends upon bodily restraint.
Note that point 3 is only a tentative conclusion: you have identified a pattern/relationship, and you are going to explore it further. Your paper should keep discovering new things! Your actual thesis, after you refine these thoughts, should make apparent to your reader why this pattern/relationship merits attention in the first place, and what its implications are for understanding Pym’s struggle for definition, or the value Pym places on the physical realm, or the implosive quality of hubris, or some other thing. If your thesis is true, then it will have ripple effects.
PS: This handout from the Writing Centre might also be helpful. Their thesis, however, could really only be argued over the course of a book-length study. This assignment is much smaller. Be creative and provocative.