Using Anglo-Saxon accounting doesn't mean you have to set the inventory valuation as automated. You can still do it manually but you need to record the expense at the time of the invoice or once a month for example. For that, put a stock account instead of an expense account on the product categories.

Here is a typical flow of how it works: 

From PO to the reception of goods in stock
=> No Journal entry

Vendor bill received and posted
Credit => Payable account
Debit => Stock account
It means that instead of putting an expense account on the categories, you need to put your stock account.

Vendor bill paid
Credit => Bank account
Debit => Payable account

Shipping to client - Sales invoice generated and posted
Credit => Income account
Debit => Receivable account

Customer invoice paid
Credit => Receivable account
Debit => Bank account

Example: Once a month, a manual entry is generated to adjust the stock account with the actual physical one (Report generated by the system: Inventory app > Reporting > Inventory valuation). Make sure the total is computed for all the products in stock.
Debit => COGS
Credit => Stock account

Note that if you have the manufacturing app, this will not create any journal entries and the inventory will adjust automatically