ozmatela:
Asking someone to diagnose why you are having pain while sleeping via an online forum is usually a recipe for disaster

. Let me provide some general comments based upon the limited information you provided and you can see if that helps.
Ever since i've been waking up with mid-upper back pain. I sleep fine during the night but wake up with soreness.
With side sleeping, waking with pain that takes a while to work its way out in your lower cervical and upper thoracic region can quite often be pillow related, and this is often a problem when a new mattress is purchased and the pillow isn't reevaluated in combination with the new mattress. Upper to mid thoracic issues can also be related to the pillow, and also can be alignment related. This can often be due to too deep of a comfort cradle (padding layers), layers that aren't substantial enough, or perhaps a support core that isn't strong enough (generally not as common with adult support innerspring units and those of a more "mid" BMI). Height/weight, pre-existing health conditions, female/male, somatotype, or what your mattress is placed upon can all influence componentry to choose.
What's strange is that i've never had these issues before and all of last year i spent the year travelling. So i slept on hundreds of different mattresses (some pretty bad ones too!) and never had an issue.
You probably didn't spend two months on the same mattress if you traveled a lot, so the comparisons to your current mattress may not be the best way to relate one model to another. Something that you slept upon for 3-4 weeks at a time would start to be a better time frame to use as a comparison.
I'm not sure what my mattress was beforehand but it would have been some sort of innerspring with a thin foam layer.
If you are aware of the layers within your old mattress and it was thinly padded and you had no issues, then it may well be that this current mattress uses a bit too much comfort material or it's a bit softer than what you prefer. I can't tell from the information provided on the website you linked to what the thickness and ILDs of the foam layers used might be to get an idea of how hard or soft overall the product might be designed to feel.
This new mattress seems to feel firm (i can't really tell to be honest) but the foam in the comfort layer does seem to give enough to sink a little.
One thing I recommend is to separate the feel of the surface comfort of the mattress ("hard" or "soft") and separate that from the deep support (mostly provided by the innerspring unit where people refer to a bed as "firm"). The comfort layers within a mattress are usually the weak link. Based upon the more basic information on the website, it appears that the innerspring unit would be adequate for those within a more "mid" BMI range. The surface comfort of this appears to lean more toward a bit of a "plush" combination, but I wouldn't be able to tell without the product in front of me. The odd thing is that sometimes a mattress that is designed to feel "plush" can actually start to feel "hard" to people, as the padding layers are so soft that the person can "feel through" to the support unit, and the mattress can actually feel "harder". This depends of course upon a person's sensitivity to localized ischemia and pressure points, mass, strength, flexibility, among other things.
I do notice some pressure on my rib cage in the morning.
If you were sinking in too deeply with an "excessive" lateral curvature, this could be from the comfort layers being "too soft' or "too deep" for you, or from the support characteristics of the mattress (mostly the innerspring) being inadequate (this could be the case if you have a higher BMI). We are in an environment with gravity, so we will always have pressure points, and if a mattress feels "too hard" it might not contour well and be poor at pressure point distribution. I don't think this is the case based upon the feedback you provided, but again that is a (slightly) educated guess

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I see the mattress you bought has a 100 day return policy, so hopefully if you think it's not the mattress for you it can be exchanged or returned.
Good luck!