Opioids are similar when it comes to being painless. It compares to Nembutal. SN is mildly discomforting so I wouldnt say it compares to it unless you took the opioid via the mouth, in that case you might vomit similar to SN.
Benzos plus alcohol are also an interesting mix. Ive never heard a story about it working, but people do warn about it because you'd die in your sleep.