Workflow for Invoice without an order

Workflow for Invoice without an order

Hi, 

I'm wanting to set up a 2 step approval for invoices above a certain value but not sure how to go about this.

Currently I have 3 bandwidths in my workflows, with the final one being 
If Invoice value exceeds 5,000 - Approval to "X"

What I want to do is send this to 2 people (as the person who has the authority to approve the value does not necessarily run the department where the budget lies) 

So, in IT for example - any invoice exceeding 5k I would want to go to the IT Manger to view & give 1st approval but then for it to be finalized by approval by a Director.

How do I do this please? 

Thanks
Jo