Mattress is quite firm

We received our new mattress and immediately noticed that it was not level -- lying on my back I was not facing straight up to the ceiling but was tilted in towards the center. I weigh 115 lbs and this was with just me in the bed. Got the level out of my tool kit and discovered that even with no one on the mattress, the mattress itself was indeed not level; the edges were higher than the center. Thinking it might be the foundation (purchased new w/ the mattress), we put the mattress on the floor -- nope, it was the mattress itself. The store kindly replaced the mattress and fortunately, the replacement did not have this crazy problem. However, the replacement mattress (supposedly same exact model) is noticeably firmer than the last mattress (and also firmer than the store model that we tested out). I have never spent so much money on a mattress before and this lack of consistency/ quality is alarming. Wishing now we chose something else--at this price we were hoping for "wow" but it is really just "eh" and now we have to spend even more for a topper since it is too firm.