Vendor Bill Approval

We have a mixture of Bills – It’s is policy that Purchase orders be raised for goods and services where possible.. However, that said, there are always bills that will never fall in convenient categories. These include Utility bills and professional fees which cannot be determined upfront.
I’m a new user (relatively speaking) We have no super user in house so I’m scratching around alittle in the dark..
When I began here in purchase ledger , I started logging all invoices on an excel sheet so when I physically passed invoices out for approval I knew who they were with and, should a supplier call, I could assure them all was received and moving forward - just waiting approval.