Hi HighVolt29,
Welcome to the Mattress Forum! 
I wouldn’t be able to tell you why there was a large difference in the two models you’ve received in your home. While there is always a bit of variation in foam when it is poured, it sounds like yours was a “night and day” difference. The obvious thing to check would be looking at the law tag to see if you did indeed receive the correct mattress, and also to check the date of manufacture, just in case you had received an older model. I don’t know if you were able to do that.
Some of the difference you may be feeling in the new Tempurpedic may be from the “false firmness” that any new mattress will have, and the foam softening that your four-year-old mattress has already gone through. A mattress will go through an initial break-in period where the foam softens over the first few weeks at a more rapid rate and then this is followed by a more gradual softening over a longer period of time.
Another difference will be in the actual specifications of the mattress. Your old Cloud Luxe specifications were more than likely the ones listed in post #1 here. The new Cloud Luxe, while Tempurpedic doesn’t share exact specifications any more, has a bit of a different configuration, and is rated to be quite soft on their scale. The Cloud Luxe Breeze (not sure if you got this versus the Cloud Luxe) is a “little” closer to your old configuration as far as layer thicknesses, but there is a difference in foam densities. It is also listed as quite soft in their line.
As both Cloud Luxe models are listed as quite soft in the overall Tempurpedic line, I would give the new mattress a chance and see if it softens to your liking, as you should have a 90 night trial. But either model will be different form your old model, so even when “broken-in” it will have a different feel.
If you do decide you want to use a topper, you could of course do so with a memory foam or latex topper to provide extra surface comfort, but realize this will “temper” the break-in of the Tempurpedic. Personally, I’d try and use the mattress itself without a topper and try and accelerate the loss of the “false firmness” of the new mattress by walking on it on my hands and knees or rolling around on it. If after your trial period you decide this this model isn’t soft enough for you, then you certainly can try to approximate that feel by looking at other memory foam options (see post #21 here for a list of site members who offer good quality memory foam products), but I’d personally hold off on that until you’ve given your new mattress a chance.
Phoenix