Mattress recommendations (pre-CPAP!)

I got diagnosed with moderate sleep apnea recently, but I won't be able to get a CPAP until September at the earliest. I'm also moving soon so I'm using this as an opportunity to replace my current 5 year old mattress. I know that a mattress isn't going to effectively treat sleep apnea, I just want to increase my sleep quality as much as possible. Does anyone have recommendations for a good, non-spring mattress? I'd prefer a "mattress in a box" set up for easily moving without elevator access, but if that's not recommended for quality reasons, I'll take a mattress that comes not all smushed up. Options for purchase in the US, please!