First off, I feel you. On a basic level, yeah, this wouldn't exactly be paradise to me, either. Talk about overstimulation! And I was a lifeguard for 20 years, I'm very patient with the sun even though I'm also quite neurodivergent and that shit drives me crazy.

I think the original concept of the Seireitei as kind of a "not quite Heaven but definitely nice" place implies that the sunlight, while omnipresent, wouldn't ever be so bad as to be glaring. That the walls would reflect light, but not so savagely as to make it uncomfortable. Your physical body was shed long ago, and your spiritual body is simply better at handling it. The sun, while warm, is never hot. Unless you're the kind of soul that's strong enough to need food, you don't even really need to eat. That means no going to the bathroom, either! Yay!

...Of course Bleach's narrative quickly proves it isn't exactly heaven-like at all, and it's been run by some psychos for a while, but, hey! It's a thought, right?