I'm running out the door, so briefly, morphine. The BA is pretty low with morphine taken orally, so I think plugging's the way to go, but I totally understand if you're uncomfortable with that ROA.
I always get a really warm, relaxed feeling from Hydro, CWE'd. But it does make me nod sooner than I'd like. I'm not big on the nod usually. I'm one of those people who usually likes to get out and do things on opiates.
But you're looking for the warmth and the nod, so hydro sounds like it might be the best option for you. And if you can enjoy codeine you will probably be able to get by with a relatively low dose of hydro. And you can re-dose during the day (with lessened effects of course) to prolong the high.
But be careful if you re-dose. I'm a long-term opiate user and I was doing about 160-200mg OC a day, spaced out into a few doses. I had taken maybe 80mg of Hydro, CWE'd, in the morning. Low dose for me, right? Then I went to a presentation by a guy whom I was meeting for the first time. We were potentially going to work on a large project together with a larger team.
I was totally energized and feeling fine when I got there, ate 2-3 5/500's before going into the lecture so I'd be calm when I was introduced to him 8). And fuck me if I didn't start to nod during the fucking presentation. It was boring and the room was hot and stuffy, but damn. He was a older, drug-naive (I hope) environmental scientist so it was ok, but I was shoving my knuckles into my eyes the entire time. I got the project though. :D