Hey Teevert.
Welcome to our Mattress Forum 
That’s great to hear your old Perfect Sleeper has held up well! Serta has made quite a few updates to the line over the years, so while the newer models may be similar in feel, there could be differences in materials and construction.
If you’re set on another Perfect Sleeper, it’d be helpful to check the specs on the model you’re considering (things like foam densities, coil gauge, and comfort layers) so you can compare them to your current mattress. Some folks have noted that newer versions of certain brand name beds may feel softer or have more motion transfer due to material changes.
Your Cuddledown topper should work well on a new mattress, but it may slightly alter the feel depending on the firmness level you choose.
If you haven’t already, we’d also recommend you take a little gander at our Mattress Shopping Tutorial and Durability Guidelines in case you’d like to be armed with some extra information!
And, of course, we hope anyone with current and relevant experience is able to chime in.
NikkiTMU