Hi mchotin,
It may be worth testing mattresses that use good motion isolating materials (including pocket coils and the various types of foam) to see if you really need a split mattress to accomplish the motion isolation that is “enough” for you. Memory foam in particular is a very motion isolating material and latex also does a great job (although memory foam is a little better in this regard). Of course a split mattress would be the most motion isolating of all if nothing else was “good enough”.
[quote] We have already visited Nest Bedding and Mancini’s and were leaning towards the Bed In a Box Serenity Gel or a Serta iComfort (a plush-firm model) but after reading the site are rethinking.
Based on my reading of other threads I’m thinking that since my wife sleeps hot, latex over coil might be an interesting place to start. And of course we’ll need to look into the mattress protector and other bedding components.[/quote]
It’s good to see you’ve been doing some good research and are cautious about mattresses that use lower quality/density foams. A pocket coil/latex hybrid would generally be a very good option for temperature regulation … particularly if it included a breathable quilting material such as wool.
If you decide to purchase a split king mattress I would probably tend to choose two mattresses that were the same height in the first place. If you have similar needs and preferences then each twin XL mattress could be the same and if your needs and preferences are different then it may be a good idea to consider two mattresses with the same layer thicknesses in the mattress but different firmness levels in the layers. It may also be worth testing a mattress where each half of a king mattress is customized for each of you so there is no “gap” in between the two mattresses as long as the materials are motion isolating enough for you. The first part of post #2 here has more about the different ways that can help a couple whose body types, sleeping positions, or preferences are very different from each other.
If you do decide on two Twin XL mattresses that are a different height then you could add a layer of very firm polyfoam in the appropriate thickness underneath the thinner mattress to bring the sleeping surfaces to the same height but I would only go in this direction if there were no other better options that that met all the criteria that were important to you.
Phoenix