I want to respond again a bit more fully this time, giving some more ideas. You say the oxycodone is becoming quite ineffective in managing the pain, and you think that switching to another opioid analgesic (painkiller) would be best. That may very well be. I often recommend that those in chronic pain look into morphine, either IR or ER, but because of your particular situation, I am not sure it would help much more than the oxy, and I would actually guess it would help less. Opiates themselves can cause headaches due to the fact that they cause histamine release and increase intracranial pressure. Morphine is one of the opiates that is known to cause a very prominent histamine release, and sometimes very bad headaches. I am not saying it couldn't work, it could work well, but I would try different meds first if I were you. I said I thought a fentanyl patch might help you, and I do, but this will quickly jack up your tolerance, though it seems you really need relief, so I'd consider that option. I don't see hydromorphone or oxymorphone working much better than oxycodone at equipotent doses, that meaning you might as well up your oxy dose. You could try buprenorphine (Suboxone, Subutex, Temegisic). It is long lasting, and it quite potent, with good analgesic (painkilling) properties. Again this would hike your tolerance up a bit more quickly. Another drug I wouldn't write off, but normally wouldn't recommend is methadone. It is very long acting, relieves pain, and is quite potent as well. A breakthrough med might be necessary regardless of what opioid you are taking for "main" control, so you could stick with Percocet or switch to non-APAP oxycodone in an IR formulation for that. If you do choose buprenorphine, an opioid breakthrough med wouldn't be effective, and it might not be so effective if you choose methadone.
A good med, as I mentioned before, might be a butalbital product like Fiorinal or Fioricet etc. Butalbital is a barbiturate, and barbiturate addiction is one of these most dangerous and hellish addictions to have, but if you used it only for breakthrough pain, I could see that working fairly well. Gabapentin (Neurontin) really is a good option, and has generally fewer side effects than pregabalin (Lyrica). I would seriously consider adding the Neurontin to your opioids meds to really subdue the pain. Also look into some unorthodox practices like accupuncture, refelxology etc. There is nothing the right drugs can't help. As mentioned above, cannabis could help as well.