Hi MJ73,
It’s not likely that a solid core vs a split core would make any perceptible difference in most cases but this would also depend on many factors (such as the type of materials, the location of the split, the differences between each side of the split, and the types of materials and layers above the split and on the ticking and quilting of the mattress).
It could be part of the adjustment period, a symptom of being too firm, or a symptom of being too soft, or an alignment symptom based on how you interact with the specific design of the mattress. The challenge of course is to figure out which it is so that any fine tuning or refinements can change things in the right direction.
I would make sure you have read post #2 here which I linked earlier. Post #3 here and post #6 here and post #6 here and post #7 here may also be worth reading to give you some insights into what may be happening and help you identify what your next “best” step may be.
I think the real issue though stems from here …
because it’s not possible to “duplicate” another mattress using different layering. When you use different layers to “approximate” the feel and performance of another mattress … how well the “approximation” succeeds is relative to each person. While there are many “pathways” to a similar outcome (see post #3 here) … each one may feel similar to some and not to others. Some people with certain body types or sleeping styles or perceptions may say “it’s exactly the same” and other may say “it’s completely different”. In some cases … because our memories for the subjective “feel” of a mattress can be so inaccurate … even the same mattress may feel very different when you’ve slept on it for a while if the store testing was based more on how it felt rather than more objective testing which tends to be much more accurate (although even here there are no guarantees either). Taking enough time for a mattress to break in can also make a difference.
For example … your mattress has a very similar top comfort layer to the Beautiful. This alone may be enough for some people to call it “very close” regardless of the rest of the mattress. the Beautiful then has 3" of 24 ILD under the top layer and then a 6" layer of 36 ILD. One possibility to “approximate” the effect of having a soft layer and then a firmer layer under your 3" of 19 ILD would be to use a softer core which would be “in the middle” of the two. an even larger number of people would call this “similar” but there would still be many who didn’t. All of this is relative to each person’s perceptions and the limitations of the design you are using to approximate another different design.
I personally think that trying to duplicate another mattress can often lead to disappointing outcomes for many reasons and it’s much more “accurate” to measure any mattress against more objective standards (see post #2 here).
In any case … I think the next steps would be to first give it enough time (and eliminate any obvious possibilities mentioned in some of the links) … followed with deciding if your goal is to “duplicate” the Beautiful (and your best option here may be to buy the Beautiful itself) or whether your goal is to fine tune the PPP (Pressure relief, Posture and alignment, and personal preferences) regardless of whether this produces exactly the same “feel” as the Beautiful (which also may have produced “symptoms” when you actually slept on it). My personal thoughts are that your own experience would be much more important than trying to “match” your subjective memory of another mattress but of course what is most important for each person is for each of us to decide and there is no right or wrong here.
Hope this helps.
Phoenix