Opana is twice as strong as oxy, orally, more or less. If your tolerance is low you should definitely feel them, and I find it to be a great med for pain control, personally. The trouble with urinating on the ER formulation might be less of an issue with the IR formula, seeing as how it isn't continuous release, so you can pee before and after you dose, and this may be less problematic for you. Healthy kidneys will produce 2-ish oz of urine an hour, so things shouldn't get too uncomfortable for you.
If you don't note sufficient pain control, try eating them with something fatty--peanut butter on crackers, heavily buttered toast, wash the pill down with a milkshake, etc.
The issue with rotating you with vicodin is...do the 10mg vics control your pain sufficiently? If not, he'd have to script you multiple pills a dose which most doctors won't do, or put you on Zohydro, which is going to probably be quite expensive.
Your other options would be probably oxy 15 IR, or 15mg morphine IR. It just depends on what the doctor is willing to do, some seem to refuse to script certain medications for reasons that are... IMO unfathomable.