Hi yazfan,
Thanks for sharing your comments and feedback on mattress #3 … I appreciate it 
As you know you made a great quality/value choice but of course that’s only meaningful if you sleep well on it so hopefully the BME will be a better “match” for you in terms of comfort, firmness, and PPP than your previous two mattresses.
Your mattress is about 1/2" out of spec in the width (see here) but it’s not unusual for a compressed mattress to take a few days to fully expand.
You will sink in less on a firm mattress than on a softer mattress so the edge would be firmer but the sleeping surface of the mattress would be firmer as well.
I’m looking forward to any additional updates you have the chance to share once you’ve spent a little more time sleeping on your mattress.
Phoenix