Congress.gov is a broader website that covers both chambers of the Congress. However, you might wish to focus on one chamber over the other. Each Congressional chamber has their own website consisting of legislative history, information about members, committee infformation, and hearings.
As you investigate your chosen issue, you should think about what federal government agency would have oversight of it. For example, if your issue is related to the environment, you should exmplore the EPA's website for any policy briefs or reports that are speicifc to your issue. Withfin each of these websites, they will have a section dedicated to publications, policy, or regulations. These will be the official publication of the agency/department providing you with informaiton on your selected issue.
For example:
If you choose to examine your issue at the state level, you should look at the state level agencies. Find informaiton on your issue at the state level by looking at the agency/departmental publications and policy briefs. For exmaple, the state of Ohio has simlar agencys/departments as the federal level.