Hi JamesOH,
Like Jeff I also don’t know which of their current mattresses would be closest to your mom’s Posturepedic mattress and the only way to really know for certain would be based on testing the current Posturepedic lineup in the store so you can identify one of their mattress that “feels” similar to you. I would also echo Jeff’s comments about the wisdom of buying any Sealy mattress (or any major brand) no matter how it may feel to you.
Major brand mattresses that are available today tend to use much lower quality materials in the upper layers of their mattresses which generally soften or break down much too quickly and I would tend to avoid any major brand mattress or any mattress where you can’t confirm the quality and durability of the materials inside them (see the guidelines here).
There is more about the most important parts of the value of a mattress purchase in post #13 here that can help you make more meaningful quality/value comparisons between mattresses.
While the most important part of the “value” of a mattress purchase is comfort and PPP (Posture and alignment, Pressure relief, and Personal preferences), outside of PPP a mattress is only as good as its construction and the quality and durability of the materials inside it and the durability and useful lifetime of a mattress is also a very important part of the value of a mattress purchase. No matter how it may feel in a showroom … there would be little value in buying a mattress where the use of lower quality and less durable materials leads to foam softening and breakdown and the loss of comfort and support much too quickly after a purchase and the loss of comfort and support it isn’t considered to be a defect and isn’t covered by mattress warranties (see post #174 here).
Phoenix