Keep it and get a softer mattress cover for it,firmer mattresses last way longer than soft ones and your back will thank you for it. I bought a new memory foam one last fall and it showed up super firm, I bought a 2" soft cover for it and now its perfect and will last for years unlike the last coil spring pos.

Also those floor models are broken in from thousands of people laying on them, that's what yours will be like in a few months.