Kinda late to this post, but to me there's much in post-rock that's more hopeful than sad.
Although fair disclaimer, some things that other people around me feel as melancholic comes across as more wistful to me.
Still seeing and agreeing with Jack's mentions I'd thought to add some more:
Sigur Rós seems to be the most obvious: they Jónsi even sings in what he dubs 'Hopelandic'. Takk was my starting place there.
Spurv from Norway mostly turns to nature and makes it feel uplifting to me: the song Til en ny var and the EP Skarntyde I can't recommend enough.
Baulta from Finland definitely have some songs that are really sad, but they also scratch the same itch as God is an Astronaut and they've got a good sense of humour too. So try Pure Escapism.
Yndi Halda has their first album called Enjoy Eternal Bliss (and the bandname is the same but in Norwegian I recall) ... so it'd seem to be a no-brainer for me. I love them and tend to listen to both of their albums if I'm in the mood for music a bit more on the lighter side of Godspeed You! Black Emperor (who start all their live shows with the 'Hope Drone', but I'm guessing you might be familiar with them already from your description)
65 Days of Static (or 65dos) and Maybeshewill I'll lump together here because they tend to be my go-to's when I want the uplifting energetic side of post-rock. 65dos in particular has been one of my all-time favourites:
Suggested:
65dos - Wild Light
Maybeshewill - I Was Here For a Moment- Then I Was Gone (earlier albums are a bit more punky and newer albums are a bit more atmospheric if you want to find more)
MONO are probably my most favourite band, but lots of their catalogue might also seem sad. Their latest works however tend to be more hopeful than sad. So you might lie to try Oath and Snowdrop
If any of the above hit the mark then the following might be up your alley too:
Ef - We Salute You, You And You! and Give Me Beauty or Give Me Death (don't let the album title discourage you. 'Hello, Scotland!' is like my personal anthem to slow uplifting feelings (especially the newly recorded version)
Hazards of Swimming Naked - Take Great Joy or Our Lines Are Down
Endless Dive - A Brief History of a Kind Human (for if you dig the 65dos/Maybeshewill vibes)
Nordic Giants - Symbiosis
Overhead the Albatross - Learning to Growl (I really love 'I Leave You This' but since it's an album dealing with grief it might not be what you're looking for, albeit in a ''celebrate life" kinda way)
Leaning more to the classical side of things:
Esmerine - Dalmak
Jo Quail - Invocation / Supplication
Hope this helps ... if not than I'm into sadder things than i thought 😃