I've heard of ozium but mostly in the context of other dank smells lol but I wish I would have known about that several years ago. We had to exhume a body that was three years in the ground for one of those mesothelioma autopsies and even though there was a concrete vault water still got into the casket. The body was GREEN. Like a darker shade of Hulk green. And the lining of the casket was caked with mold. When we opened it, whatever we were spraying was not working. The only thing that helped was some mint stuff to put under our masks. I have never smelled a worse smell in my life ten years later and like with the OP, it was a smell that just lingered in my senses for days.

Try vicks vapor rub or a mint balm above your lip. Worked with dead bodies before, and that always seemed to help with the smell of decay somewhat.