Hi Phil P,
Thank you for providing that contact information for poetailor. 
You and your wife are a good example of how seemingly small differences can make a significant differences in comfort perceptions to some people. 
Unfortunately, it’s not possible for me to “diagnose” mattress comfort issues on a forum with any certainty because they can be very complex and there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress in terms of “comfort”, firmness, and PPP or any “symptoms” they experience. However, there is more good information about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here .
Starting with your shoulder/neck region, I would make sure that your pillow is appropriate in thickness for your new mattress. As you stated, you’ve always had some issues here, so it’s important to double check this, as you don’t want your head to be too elevated, or not elevated enough. This is especially important when sleeping upon your side, as research has found that the majority or lower cervical / upper thoracic issues tend to be pillow related.
As for the hip tingling, this could be from either the upper comfort layers being “too soft” for you and you’re “feeling through” to the innerspring unit, and the pressure there is enough to cause discomfort, or capillary blood flow issues. Or there may not be enough padding on top for you to create enough of the “comfort cradle” that you desire. Or, the support of the spring unit could be allowing you to sink in too much when you are on your side and could be allowing for some alignment issues. This is a good innerspring unit, so I’m guessing that it’s not an issue of the support unit, but more of the comfort layers and also your adjustment to the new mattress.
As you mentioned, you’ve only had the mattress for a few weeks, and I would suggest that you try the mattress a bit longer and see if your body adjusts better to the new mattress and loses some of its learned alignment.
I wouldn’t use the “softness designations” of the two different brands as a reliable relatable scale of how one will compare to the other, or how the firmness of the Brentwood would predict how the firmer Eco Terra might feel, as they are different products using different materials. I would only compare what you currently have to the firmer version, which would use 29-31 ILD latex (versus your current 24-26 ILD).
I appreciate the creativity of your photo, but unfortunately the placement of a weight upon a mattress can’t provide any meaningful information about the appropriateness of the mattress for anyone, and your own personal use of the mattress would be the most reliable indicator you can have.
I hope that you’re able to try out the mattress for at least a few more weeks and I’ll be interested in learning about your perceptions of the mattress after that time, and I hope it becomes more comfortable for you.
Phoenix