Hi Rorarie,
This is an interesting request.
Do you want me to guess how many people and how big and what parameters?
I do have a good imagination. :)
There are a lot of new types of mattresses that I have no experience with including some with multiple layers of different materials like silicone rubber and memory foam.
My favorites have been innerspring mattresses. The foam usually gets too hot, plus I, personally don’t like the feeling of sinking into the foam which then makes it difficult to turn over. So a reasonably supportive, if not firm, innerspring has worked well.
But if purchasing one in the US, be careful! Buying one here is worse than buying a used car. Try to find a very reputable vendor. The major department stores and brand names tend to be better, but wrt the discount “mattress stores”, watch out!
My favorites have been the two I purchased from Dux stores, an upscale, Scandinavian brand, especially the Dux3001. Not cheap, but so durable, and well thought of, that people bequeath them in their wills.
But bear in mind that mattress comfort is a very individual thing. What one person finds consummately comfortable, another person may find totally torturous.
I think the OP is long gone, but as much as I also hate foam and especially memory foam, it may well be of benefit to those who have a partner with sleep movement disorders, for the very reasons you describe.
Quality modern innerspring mattresses sometimes incorporate these materials in their external layers.
I have been a big fan of Simmons Beautyrest pocket coil mattresses. However the last mattress we bought was from Costco. It is their Kirkland Signature by Stearns & Foster. It is firm but comfortable to us. There are a lot of things about a mattress that are personal preference of course. We got a king size this time, and due to the size and thickness, it is a bit of a monster. The delivery people who were to bring it to our bedroom were real close on giving up on getting it up to the second floor room. But with my help the three of us managed to get it up there. If it has to be replaced I would not buy the king size again, but instead would buy two twin XL size mattresses so it would be easier to handle. Still should be able to use king size sheets and make it up like a regular king size.
With a CPAP I think pillow choice is probably more important than a mattress type. I used to use one of those shaped memory foam ones, but found it pushed back too much when I would sleep on my side and my mask was pushing into the pillow. I have settled on a Beautyrest Platinum down alternative pillow in a satin pillow case. The down alternative forms to my head better and does not push back. The satin pillow case which is really a zippered pillow cover allows my head and mask to slip around without the pillow pushing it off my nose and losing the seal.
But, all of this is mostly personal choice. It hope that helps some.
It seems that you can still buy Simmons Beautyrest, even in Tasmania.
Our mattress down here is a monster too, so much so that we will probably have to dispose of it eventually.
We've had it for almost a quarter of a century now and it's still a really nice mattress but it's so thick that it's hard to find linen that fits and it's so heavy that it's hard to lift to make the bed.
We bought it for a song from the manufacturer at an industry trade show and I think they discontinued production shortly afterward.
It looks similar to this one but the topper is separate (clipped in place) and the mattress and topper are both reversible.
I've bought dozens of mattresses in the intervening years (for work and family) but never seen one quite like it.
Fortunately, the newer mattresses are a lot lighter.
The split mattress approach is more flexible and forgiving, especially if you are dealing with an awkward stairwell or close corners. For anything larger than a queen, I would vote for using the split box spring and mattress with a unifying topper to avoid the “crack’ in the middle, unless you also require the flexibility of separating the king into two twin width beds.
I agree about the split mattresses.
We use one at our residence in another State.
It's a reasonable quality, affordable, commercial model that zips together so there is no crack.
When they are unzipped the gap between them isolates movements and it's a great spot to 'lose' the grandchildren. :)