Generally, original literary research projects are quite narrow in scope and respond to an existing gap or problem in the study of literature. Since the only way to figure out what has not been done is to be intimately familiar with what has been done, the more broadly and deeply you read in your chosen literary field, the more likely you are to arrive at original ideas.
The first thing you should consider when selecting an area for research is your own skills and knowledge. As there are many literary critics writing about English-language literature, as well as about literatures associated with major western languages, if you know a language with a small number of native speakers, that would provide opportunities to do original work.
Even within English, the best known authors tend to be widely covered in existing criticism. It is quite difficult to do original work on Shakespeare or Chaucer because thousands of books and articles have already been written on these authors; you are more likely to be original in writing about less well known authors.
The type of research most likely to be original is that which works with rare archival materials. For example, many newspapers print reviews of books and plays; some also print poems and other literary works. You might look at a single local newspaper published in your town and read through a full year's print run and then do an analysis of all the literary materials that appeared in that newspaper over a year. Such a study would reveal the popularity of and attitudes about many types of literary works. Another possibility would be looking at a single day over a period of fifty years, say 14 February 1900 to 2000. You might use such research to talk about shifting literary visions of love over that period.