Specifically, I'm looking for bands such as Colosseum, Doom:VS, the first half the Black Sun Aeon's "Routa", and Swallow the Sun. Also Forest Stream and The Foreshadowing, at a stretch.

Other than these bands I've never found something polished enough and emotionally satisfying to keep me engrossed for a whole album. I've tried to get into Nox Aurea and Saturnus a few times, but they seemed too generic for me when I was giving them a listen.
Keep it either modern doom/death or funeral doom also, as I doubt stoner or traditional doom has anything in terms of what I'm looking for.

Anyway, it'd be good to see what you guys've got.

An obvious rec would be Dawn of Solace if you like Black Sun Aeon.

Other than that, there are tons of Doom bands out there that play that kind of soft, mellow, gothic-tinged music. Yeah, tons...
don't know, maybe give a try to Black Wreath, they're most unknown, but very good at what they do (funereal death doom).

We now have TWO doom help threads, I'm sure you could use them.