Hi iambatman212.
Welcome to our Mattress Forum. 
It’s always disappointing when a product tha6tt works for you is discontinued. Sometimes this may be a blessing in disguise especially when foam breakdown, durability, and useful life a mattress are involved.
With some digging, I could find the layer specifications on the Simmons Beautyrest World Class - Corita Plush. This is not the first time Corita has been discussed in the forum. The Corita Plush has 3.75" of 1.2 and 1.5 lb polyfoam in the comfort layers which raises flags as a weak link in terms of how long this mattress would last as this will affect how long you can sleep well on this mattress regardless is this is a good fit in terms of comfort/support needs for your particular needs and preferences to start with.
The comfort layer(s) specs for their recommended replacement are…
• 1.25" AirFeel Foam
• 1" RightTemp Wave Foam
• 1/2" Beautyrest Gel Foam
• 1.5" GelTouch Foam
Adding up to 4.25" of polyfoams for the comfort layer. I doubt a quarter-inch of difference is going to matter much as far as “feel” goes, but the foam densities and IFDs certainly do. Unfortunately, I couldn’t find the foam densities, but I doubt they’re much higher than the 1.2 - 1.5 lb polyfoam that was being used in your previous mattress. I would stand clear of any product for which you can’t find the density of the foams and constructions.
I wouldn’t factor the reviews of others into your decision to purchase any particular mattress. People often review mattresses far too early after receiving them, and reviews lack specific information about all the variables that can contribute to the suitability of a mattress (like details about the person and the mattress) that would make them more meaningful/accurate. I’d suggest reading about the dangers of making a purchase based on reviews here. The same goes for review sites that more like revenue sites.
I’d be more hesitant to pull the trigger simply because we know their previous models carry low-quality foams, and they lack transparency about their foam densities as a rule. I suggest before moving ahead with any purchase that you learn a little bit more about the materials that can affect the useful life of a mattress in our Mattress Durability Guidelines here. I’d also recommend taking a look over Mattress Specifications You Need to Know and our Mattress Shopping Guidelines.
It’s very possible the Harmony Lux will serve you just fine for a limited amount of time, but it’s always good to go into a new mattress purchase as informed as possible to be able to estimate how long you can reasonably expect a mattress to last before any foam breakdown that can compromise your spinal alignment and quality of your sleep.
would allow me or any of the mattress experts on the site to offer a better commentary on this mattress for you.
Looking forward to any questions or updates you may have.
Phoenix