I did a ton of research on mattresses when getting a new bed two years ago. Casper was my first choice since I heard so much about it from my startup friends. I wanted one that was biodegradable with no off-gassing. I took a deep dive into Casper's safety claims and it opened up a whole can of worms.
I've never seen an industry with so much greenwashing. The organizations that certify the mattresses as being safe are comprised of the suppliers themselves. They are basically chemical companies pushing cheap non-biodegradable foam with crazy markups under exotic brand names. Casper just sells this cheap foam with questionable safety standards like everyone else. The only standard I found not to be shady was GOTS [1].
I ended up making my own mattress from slabs of organic latex. It was cheaper and more comfortable than the Casper anyway. Now when I have guests over I can easily remove a layer and have another temporary mattress. They ship compressed and rolled up in boxes which were way smaller than the Casper one. (Btw, the box advertised in Casper ads and in their showroom is nowhere near the size of the actual delivered box. It's massive). If you don't want to make your own, here's a good one: https://sleeponlatex.com/products/natural-latex-mattress.
[1] http://www.global-standard.org