I would suggest you start by identifying your topic more precisely. It should be unique, of potential impact, and viable because you have identified appropriate data which you can access and analyse. This will also involve reading around your subject area. The published literature will give you some ideas of possible literature review themes. Your objectives and research questions are other sources of potential themes. Alternatively, you should be able to describe your unique topic as a combination of three, or at most four, constructs or contexts. You have already mentioned sustainability and financial reporting, but this is currently too broad and vague for an achievable project with the potential of making a modest contribution to the body of knowledge. Read the literature on your subject and you will see what I mean when you look at the specific nature of other people's research. These three or four constructs/contexts could also inform your choice of themes.
Hopefully the views/guidance as per the following publications could help:
Bonimi, S. (2011) The Business of Sustainability, McKinsey Global Survey Result, pp. 96-105.
Chousa, J. P. and Castro, N. R. (2006) Integrating Sustainability into Traditional Financial Analysis, in Schaltegger, S., Bennett, M. and Burritt, R. (eds.) Sustainability Accounting and Reporting. Dordrecht, The Netherlands: Springer, Chapter 4, pp. 83-108.
Kielstra, P. (2008) Doing Good: Business and the sustainability challenge, The Economist, pp. 1-53.
Venter, E. R. and van Eck, L. (2021) Research on Extended External Reporting Assurance: Trends, Themes, and Opportunities, Journal of International Financial Management and Accounting, 32, 1, pp. 63-103.