Addiction to one might as well be addiction to the other, in this case. However, methadone has a longer half-life and withdrawal, so should ideally be avoided as well as you're able, an addiction to that would be worse than where you somehow managed to get to already. I, at least, am glad you don't seem to bang opiates like I learned them. You know, for me, I was using hydromorphone, so I could use poppy seed tea's morphine to assist with tapering. I don't think you have that option. You'd need tens of kilograms of seeds that you'd need to take to get withdrawal reduction alone! But if you need it for pain, I understand, just be careful. You can train your brain; a little can be quite a lot. That said, I just checked the dose equivalency for 1.2 grams of morphine (I've only banged up to a little over 300mg, well, and only while on stims (and manic), that was amazing, and 1.2g's plugged must be even stronger, if perhaps not in the rush) and found it to be apparently roughly 135mg of IV'd hydromorphone. I shot in the 120's a few times. I was pretty tolerant, to say the least. But I never regularly did that high a dose. I tried to keep it around 50-60 or so, if I could, per shot. You, sir, have achieved something quite interesting and unfortunate in reaching this level of addiction. You might need to switch opiates, to methadone, which I'd avoid if possible, or to some other opiate you can use temporarily to lower tolerance. In the long run; I have no idea where your level of dependence will take you, that really depends on you. We are only as great as our hearts will allow.
You can use oxy in place of methadone, or methadone in place of morphine, it's all the same in the brain, for the most part, just to fully clarify. But you need help, and I don't know where to send you, because my tools are null in your situation, and I despise the idea of rehab, not to mention your implication that mobility is an issue due to pain. Try to reduce your dose/tolerance.