The UN's Sustainable Development portal has a wide variety of information. However, several sections of the website will be especially useful to you:
These are general resources that will be useful to most people for more topics.
These resources are often useful for researching a specific goal. For example, GreenFILE would be useful for goals related to climate change and life in the oceans. If you have questions about which resources would work best for your topic, please contact Blake.