Your probably, more than likely going to need a lot more of the morphine for breakthrough pain.. I have always found morphine whether it be ERs or IRs to work terrible when taken in the way they were designed to be, orally just swallowing them... By far the most underwhelming ROA with morphine, or about on par with intranasal, Both of those ROAs to take morphine IR/ER aren't very efficient IME with them.. having taken over 300mg+(not recommended to take doses that high if not tolerant to the drug, or in general to start out with when you first take it.) while being addicted to oxy at that time of oral/insufflated, mostly oral morphine, which basically just got me well, after being in oxy WD which I was addicted to at that time, taking/doing (via other ROAs than oral) around 100-300mg a day of oxy, depending on how much money I had, and found the oxy to be much stronger, taken just about any way you can take a drug, except when I would bang it.. oxy is not as good IV, feeling wise, in my opinion, as Morphine is... The only ROA morphine is good for is IV, IME trying all of them, except plugging and IM(IRs only for the pills, ERs cant easily/safely be prepped/slammed, it is very risky even if you can get past the gelling up while prepping it..), and I don't really advise you to ever IV opioids, especially if you take them everyday for pain.. It is not going to end up well, in most cases when people do this with their meds, unless they also get other opiates off the street too, and just slam as much morphine as they want, run out, and are able to get more at all times from others.. SO when I said IV morphine is the only, actual decent way to take it, I didn't mean, go out and do it, its just facts.. IV is ~100% BA with morphine and oxy. Oxy for whatever reason, is way different than the majority of opioid pain pills, because they work ALOT better oral, than they do IV imo.. Oral oxy is like around ~80% more or less, IV Oxy is ~100% but doesn't last as long, doesn't give too great a rush if you IV it, in my experience with it.. Its there, but not like morphines is.. No opioids are really going to be safe to IV, as they are already very addicting when just taken as prescribed.. when abused, like IVed, sniffed, or etc.. etc... So I don't recommend people do it.. It may feel great at first, or all the time to them that way, and you may do them that way everyday like I used to with most opis.. I take subutex now.. Thankfully..
Anyways.. sorry, I kind of rambled off there. In short, I would totally stick with the oxy! I am pretty sure you wont like the morphine IRs if you take them as prescribed, orally.. alongside morphine ERs oral.. That is just MY experience with oral morphine, and the fact is, it is not a very powerful opioid at small doses, when taken oral. Something like 30-40% or less, is the BA of oral morphine ER/IR... SO, yeah.. I don't know if morphine is therapeutic to you and helpful for pain as of now, since you have been taking ERs with oxy IRs correct? I always found morphine to be a weak opioid orally.. oxy is the best one to take oral..