@mstern, thanks for your interest in DLX and sharing your experiences – it is very helpful.
Shoulder pain is often related to the pillow, although a mattress that is too firm can also contribute. It’s best to look for a pillow with the right thickness and firmness that keeps your neck in a neutral position. If the pillow is too soft or thin, causing your head to tilt toward the mattress, it can drive your shoulder into the mattress, creating pressure and possibly leading to shoulder pain.
We believe our mattresses provide good edge support—though your experience may vary. The LatexLux likely offers the best edge support because its primary comfort layer is a 3" piece of latex. Latex is more buoyant, resilient, and supportive than other foams, which should help when sleeping close to the edge.
Keep in mind that a lot of mattresses typically don’t have the same edge support as mattresses with a border rod and edge springs. While rare today, some pocket coil mattresses still use a border rod. The best edge support comes from open coil mattresses with edge springs. I know the Saatva mattress doesn’t use this feature. We don’t have firsthand experience with the Dreamfoam Hybrid, so we’re not sure how its edge support compares to the DLX.
It’s also important to note that the firmer the mattress, the better the edge support, which could explain why the Saatva may perform better in this regard. However, Saatva uses a foam encasement around the perimeter, which can initially help with edge support, but it may break down at a different rate than the springs. In the long run, it might not be as durable. I know @Maverick has opinions on foam-encased mattresses.
Personally, we don’t believe any mattress will completely fix back pain. While some companies market their products as a magic solution, we don’t subscribe to that belief. At best, a mattress can help mitigate some of the pain.
Based on the information provided so far, we’d lean toward recommending the LatexLux in Medium. Plus, your mattress has a zipper, so if needed, we can change out the firmness or adjust anything with the 3" layer.
Hope this helps, and feel free to reach out with any more questions!