Beautyrest Black 14 Inch King L-Class Extra Firm Premium Pocketed Coil Mattress with Cooling Technology, with 9 Inch Box Spring

I went into buying this mattress thinking that it was an "extra firm" typical to my corita extra firm I purchased like 9 years ago which was a rock.! I found this mattress to be very mushy and soft akin to a plush type of mattress. I would rate this harness scale to be more like a 6 or 7 using the us-mattress scale. I found there to be no side/edge support and found that when I sit on the edge of the bed or roll to the edge to get out of it , it sinks a lot! At first I thought maybe I got a defective one. I am a plus-sized person, but this is ridiculous. There's very little support throughout the mattress and I'm going to exchange it for one with more support. I worry about the longevity of this mattress.