Full size Beautyrest mattress (Near McFarland)

I bought this mattress with a used furniture set, but prefer a firmer mattress. My understanding from the previous owner was that it was not heavily used. It's in fine shape and has a couple of spots (shown in photo), but is otherwise a good mattress. I just moved it to my garage which is where I'm taking the picture from. The model is Beautyrest Phoenix plush