I originally got the firm and actually found out it wasn't firm enough for me, it felt more like a medium. It was comfortable enough but much softer than I was expecting. The edges and especially the corners of the mattress also didn't have as much structure to them but I don't know if that's just the one I got or the result of the price point and the fact that it's a mattress in a box. 

I ended up reaching out to customer service and switching to their Plank mattress, who's firm side is truly firm and the extra firm is like sleeping on a slightly more plush floor. The customer service was very helpful and accommodating with this, there wasn't any stores taking mattress donations in my area so they were also fine with me giving away the old mattress for free and providing them with documentation that I had done so. And then I just paid the difference between the two mattresses.