well I need pretty big doses of both, but tramadol always worked better for me than codeine, but this is due to the snri effect more than the opiate one, for the opiate feeling I just add other opiates to the mix. tramadol looses it's honeymoon period over time and btw it should not take forever to kick in, the IR ones take 30 mins tops usually and the ER ones 1 hour and a half or maybe 2 hours depending on your version.
but pete I would advise just staying on codeine as the withdrawal is not as awful, tho as you CWE a lot maybe check out your liver when you got time and money to do it to make sure you ain't damaging it with "infiltrated" paracetamol