We have a report that tracks JEs and Amortization Schedules, but the only readable information about related transactions is the Created From field, which is a transaction id that could apply to Bills or Invoices, for instance. First, are there native reports that are able to show more information about related transactions? If not, were you able to solve this problem with reports or saved searches?

You can join all/most fields from Created From records. For instance on Saved Search results look to the select "Created From..." with the dots. that will then give you all /most of the available fields.