Hello:
Picking a mattress for someone via a forum isn’t something I can really do with any certainty, but I’ll do my best to address a few of your questions and hopefully my answers will be helpful to you. And there may be some other forum members who can provide some insight for you as well.
Alignment/support is the most important thing that a mattress does for you, so you’ll always want to choose something that doesn’t allow for too much of an accentuation of your lateral curvatures when side sleeping, especially with your issues with scoliosis. Generally, you’d want something with “just enough” surface plushness to assist with contouring for your shoulders and hips. I wouldn’t be able to tell you how much that would be, as there are so many variables involved, including your body type, level of sensitivity, and of course your back issues.
I don’t know that this is necessarily the case. There’s not a huge difference in mass between you two, and when someone is sleeping prone also needs very strong support, and surface plushness generally should be on the more “basic” end of things to not allow for too much accentuation of the forward lordotic curve of the low back. Between the two of you, as you have the physical limitation, I would tend to gear your choice of the product toward your specific issues.
I’m not sure what criteria you used to select your preliminary mattress brands, but whatever you choose you should be sure that the product is using high quality componentry (higher density foams, good quality construction, strongly supportive cores). That is discussed in great detail here on this forum.
As for the comfort scale you listed, realize that there is not an ASTM standardized 1-5 overall mattress comfort scale, and any numbers provided by a manufacturer are their own subjective numbers comparing one model to another within their lineups, and these numbers are not something you can cross reference empirically across brands. They are just a company’s way to help guide you, as you really can’t lie back on your computer monitor to see how a product feels!
You seem to be in a bit of a hurry to buy a mattress, which is something I try to discourage, but I understand if you’re not sleeping well. Because you have some very specific needs, ideally I’d recommend testing out items in person. While you sometimes can get good advice from chats with customer service reps from online companies, quite often they’re just regurgitating talking points provided to them and they aren’t trained about products or ergonomics. If shopping online, I recommend you try to reach someone on the phone from the company who has experience in their mattress designs and how their products fit people with different conditions. And one thing you may wish to consider would be an all latex mattress on the “firmer to medium-firm” end of the spectrum, as this can be quite supportive and contouring at the same time.
I hope that helps!
