Hi tired1.
Welcome to our Mattress Forum!
I am sorry to hear about your health issues; you certainly have some difficult challenges to deal with.
Obviously the showroom model has had more use than your new product (and it could have been at a warmer room temperature which for Memory foam comfort layer(s) would have made it feel a bit softer too), and would more than likely be more representative of what your mattress would feel like after this initial “break-in” period.
You did not specify what material and how thick the comfort layer of your actual mattress is, but generally speaking no mattress can totally eliminate pressure points, however there are certain foams, specifically latex and visco-elastic memory foams, which in the appropriate plushness/thickness can be very good at assisting the distribution of your mass over a wider area and minimize pressure points.
Given your condition, I am not very sure if you can make this work, but you can certainly accelerate the loss of the “false firmness” of the new mattress by walking evenly and carefully, or crawling on your hands and knees or rolling around on it. Doing this will stretch and loosen a little the mattress cover and also break-in the foams underneath as the entire mattress gets tenderized and the materials settle. If the mattress has a zipper cover you could also consider unzipping it and leaving it open until the cover has had the chance to stretch and break-in a little.
I would also look at any layers that are in between you and the mattress or any other parts of your sleeping system besides the mattress which may be a contributing factor. This would include any mattress protector or mattress pad you are using and your sheets. In some cases, a mattress protector or sheets can create a “drum” effect which can lessen the amount your shoulders sink in just enough to cause pressure and this tends to affect the lighter parts of the body more than the heavier parts. I would also make sure that you have a rigid non-flexing foundation or support surface under the mattress (or a support system that is suitable for the mattress) to remove this as a possible cause as well (a flexing support surface under the mattress can allow heavier parts to sink in too deeply while still being firm enough to prevent the lighter parts from doing the same).
Part of the breaking-in and adjustment period is to give your body some time to get used to a new sleeping surface that is different from what it is used to (see post #3 here ). This would typically be a few weeks but it can be shorter or longer depending on the specifics of the person and the mattress (higher density materials like latex can take longer) and it can be surprising to many people how much their sleeping experience can change over the course of the first month or so.
I don’t know if you are stuck with this design, or if you have any options of adjusting, customizing or exchanging your mattress, but you may consider looking into any after purchase adjustments that are possible such as changing thickness/plushness of the comfort layers for better pressure relief and overall comfort.
I hope this gives you a few things to try and I’d be interested to learn of your progress, how much the mattress changes for you, and what you eventually decide to do.
Phoenix