Do you need a topic sentence or a thesis? The topic sentence introduces the topic of that body paragraph. Your thesis is, simply put, your topic + your opinion. The thesis states what you are going to prove in the rest of your essay. Your thesis would change depending on what you chose to write about. You would write about the role or creator and creation, the creator's responsibility to his creation, man's alienation from society, man's desperate search for approval, revenge, Gothicism in the novel. Those are just some possible topics. Your thesis could incorporate one of these topics and your opinion of how the topic fits into the novel.
To easily create a topic sentence, take part of your thesis and restate it for the thesis. For example, your thesis states, "Frankenstein intimately explores the role of creator and creation and the responsibility of the creator to that creation." Then, your topic sentence could say, "Mary Shelley depicts the different positions the creator and creation can take."
Hope that helps!
You get right to the point, which is a good thing. A few things to consider. Shelley is writing in the 1800 during a time where there is rapid development in industry. New things are on the horizon, but this means that the past is fading away. Whenever there is a time of transition, there will be people who embrace what is new and there will be people who resist and see the dangers. With this background, you can write on a number of things.
Here is an example of a topic sentence that I might use:
In Shelley's work, there is a conflict between the positive and negative sides of technology. She explores and develops the negative points in the following ways: ...........
Here is another:
In Shelley's work, there is a tension between the one that is created and the one that creates.
I hope this helps.