Heroin is derived from morphine which is a constituent of raw opium latex but it would be inappropriate to call opium the main ingredient of heroin. It is more like wine to hard liquor, opium is to wine as morphine is to 151. For anybody in pain the opiates/opioids are your safest, most effective option as they have been for centuries. It would work out better to have them prescribed to you though since it would probably take at least several dozen poppy plants to yield enough opium for year-round personal pain treatment.
Marijuana can also be used with opioids for increased analgesia.