Graham,

We have the same problem you do or did.   We create a vendor template with all the items we order.  It's quick to create this template, just copy one of your PO's to recurring transactions and name it for one of your vendors.  Now each time you order, everything is done.  Just change the quantities and save as a new PO.  We also use https://saasant.com  to import invoice detail into QBO.  However, I don't think they offer PO's at the moment.  But you may want to check.  It may be offered now.