Look, all opiates/opioids are NOT the same. They effect difference receptors to different degrees and have highly variable half lives, overall duration of effect, presence and so on and so forth.
Per your "problem." Although it is certainly a formidable problem in your life at the moment, 30 to 40 mg of oxycodone is not a large habit. That is the good news. You need to keep that very important fact in mind as you attempt to deal with the issues facing you.
IF you were to go "Cold Turkey" (simple cease all usage with a last dosage, take no other opiates/opioids) you will be livable in 48 hours and clean as a whistle in 72, no matter what others tell you that is a medical fact. You only suffer physical withdrawal for as long as the substance remains present in your body. When you finally evacuate all of it you will no longer have physical issues to deal with (re withdrawal, not analgesia, i.e. "Pain relief" of course).
The hardest issues by far are the mental/emotional ones. These can last for weeks and considering "cravings" to be an emotional/mental aspect one can say you will always be in "withdrawal."
"Tapering" only deals with the physical really. It does cushion the "let down," mentally as well as physically but most users find it more difficult to taper because one you regress back over the noticeable threshold you will not "feel" the 10 mg (or whatever arbitrary dosage) you peter out on.
Bupe/Sub is an option (really the only one considering your low dosage, in terms of MAD i.e. "Medically Assisted Detox"), but it has an insanely long half life that means you will end up shooting youself in the foot, so to speak. To speak clearly, you will trade 1 addiction for another, 1 opioid for another, and trading for one that is exponentially more difficult to wean yourself of of.
Bupe/Sub is not really good for detox anyway, since it only has a range of 8 mgs, with 8 being the metabolic threshold/ceiling. It is also infinitely more difficult to titrate (adjust) dosages downward incrementally (meaning, on your dosage of oxycodone you would PROBSBLLY register at 2 mg. Buprenorphine as a maximum dosage, and you can titrate (adjust) 2 mgs. Bupe. Downward but so much, and all you would end up with is a nastier physical addiction.
Methadone is the substance for such miniscule adjustments but your habit does not render you an appropriate candidate for methadone detox (though IF you really wanted I am sure that you COULD find an irresponsible medical provider to dole it out). Again, possibly a horrendous physical addiction in the trade off.
IF you do not have access to lower dosages of oxycodone, like 5 mg. IR (Immediate Release), you can purchase a "pill cutter" and divide your tablets in a VERY loose approximation of 5 mgs. Each (ONLY IRs, NOT EXTENDED RELEASE, EVER).
Good luck.
