Get them shipped from Amazon. I got this one for some family who had fallen on hard times: http://www.amazon.com/Sleep-Master-6-Inch-Therapeutic-Mattress/dp/B005G02ESA/

Pretty much all of the foam mattresses on Amazon are highly rated and come shipped with all the air removed. You need to open them, let them grow back to full size and air out a little and they last forever with no issues with the sides losing structural integrity like a regular mattress if you like sitting on the edge. They also require no box spring. You can get a cheap bed frame from Amazon too for the same price as the mattress. all told you can spend $200 bucks for a full bed with frame and mattress.

They are very firm, however. Which I love and they don't wear out in the middle and form that body crater that a lot of normal mattresses do. There are options for different top materials like gel and memory foam and a few with little raised cooling towers that let air circulate under.