Visual Studio Team Services Work Item Approval Workflow - send to 'Assigned To'

Afternoon Everyone,

We've started investigating Flow for a numberof uses, inluding migrating some of our Dynamics 365 Scribe workflows.  We've also looked at using ti to improve parts of our project management process.  We currently use VSTS to manage an agile development process and we would like to use Flow to get Release sign-off from the business.  Currently I have a flow that runs as User Stories get updated, it's checking to see if a User Story is in the state 'Awaiting Business Approval'.  What I would then like Flow to do is send the approval to the user to which the Work Item is 'Assigned To', but there appears to be very few fields actually exposed to Flow form VSTS.  Is that the limit of the integration currently, or can I use the advanced editor to access a greater range of fields?

Many Thanks

Matt