Your mattress has no memory foam in it....which is why it help up so well.
Sealy used to make an excellent quality mattress, and at a reasonable price.
Today, everything they make for retail stores are nothing more than expensive junk.
I'm afraid you won't be able to find anything like your old Reserve Series Holly Springs Posturepedic.
You have to start from scratch.
When you shop, be sure to avoid buying mattresses that have memory foam in them.