I really like our SleepOnLatex mattresses (https://sleeponlatex.com). They're yet another mattress-in-a-box company, and the name is kind of bad, but the mattresses are very high quality AFAICT - UL Greenguard Gold/Oekotex certified for low emissions, organic wool covers rather than chemical retardants to meet fire standards. And they're extremely reasonably priced to boot ($800 for a queen).
No affiliation, just a very happy customer. Never tested their customer service/returns/etc, so I don't know how good they are there.
I don't know the brand, I got it from a local mattress store in town and it wasn't branded beyond the name of the store (not a chain). But neither was it made locally, I think they're mostly made in SE Asia. I assume there must be online retailers but can't recommend one, sorry.
No affiliation, just a very happy customer. Never tested their customer service/returns/etc, so I don't know how good they are there.