online - mattress - bed in a box

Looking for a mattress from the online store.

We need a bed in a box, but I prefer a firm mattress. I'm not a fan of the squishy sink of most memory foam mattresses. Got it narrowed down to the Casper Select or the NSC Medical Hybrid. 

I know that Casper is a large company so there's lots of reviews. Ruled out the Ghostbed because all the reviews are from their corporate site but the company seems to have an absolutely terrible reputation. The NSC has far fewer reviews which makes sense since it is a small company, but also not as many reviews overall out there either. Leaning towards the NSC because it is a hybrid rather than full foam mattress.

Wondering if anyone has feedback or other suggestions.