As far as I know what you want unfortunately might be a tall order. From what I know, I take opioids for chronic pain, the neurons and the like in one's brain where the relaxing feeling and the like are produced also makes a person if not sleepy, at least a lot more than just relaxed, (read sleepy).
Now I take 4mg tabs of Hydromorphone and i am VERY opioid tolerant, but still, I can take 8 mgs and it usually will help control the pain and make me feel relaxed. BUT on that rare occasion that it does not, and I take 12mgs, then BANG, I get sleepy more than half the time.
Same with me as far as klonopin goes. Most of the time even .25mg, half of a tab, makes me sleepy and a whole tab, .5mg knocks me out till the morning.
Never say never and I am also very curious if someone knows a chemical that will relax, besides alcohol.
Walter