The main lethal ingredients are Digoxin and Amitriptyline, which are cardiotoxic and bring about cardiac arrhythmia and, in the end, cardiac arrest.
Morphine serves these purposes:
- Might be lethal on its own (15g is an awful lot, even though oral bioavailability is poor)
- Promotes analgesia and deep sleep
- in combination with the other drugs, it increases the risk of respiratory and CNS depression
Unfortunately, it also slows intestinal motility and is likely to cause nausea.
IMHO, you can skip it or, even better, use another synthetic opioid (maybe snorted).
Even though Amitriptyline has a sedating effect on its own, a heavy dose of a long-acting benzo like diazepam (Valium) is required to make sure you stay asleep the whole time. The
benzo Equivalence table may help you.
Also remember there are other benzos which are legal and apparently easy to buy on research chemicals websites.