Hi cubt82,
You can see the layering of the Nature here (assuming you tested the active fusion version with the blue cover). It has a different layering arrangement with different layer thicknesses and ILD’s so it wouldn’t be an apples to apples comparison with any single ILD layer choice with a different thickness. The Ultimate Dreams also has quilting foam on top which the Nature doesn’t and the support core may also have a different ILD and is a different material which would make some difference as well. If you let Chuck know your preference for the Nature though he can probably give you a reasonable approximation for a similar comfort level. He would know better than I would how to take the effect of their quilting layer into account and perhaps the difference in the firmness and type of core as well. My guess is that a 24 ILD choice would be a bit softer and the 28 would be a bit firmer but this would also depend on your weight and sleeping positions because these will make a difference in how far you sink into a mattress and how much of each layer you would feel with either mattress. If in your conversation with Chuck you are stuck in between two choices then I would tend towards slightly firmer rather than slightly softer because it’s much easier to soften up a mattress that is a little too firm than to make a softer mattress firmer.
There are some good foundation options in the foundation thread here (including one from Walmart that is the same as the one you linked) and Brooklyn Bedding also has one that is better yet for a slightly higher cost. With the wire grid foundations I tend to prefer one that has more wires so that there is a more evenly supportive surface and there would be less risk of the wires impressing into the base foam over time but your mattress has a polyfoam base layer so if cost is the primary factor and you are OK with the slightly higher risk of the wires impressing into the foam because of the wider gaps then the one you linked would probably be OK. They haven’t been out for long enough to really know for sure so my preference is more because of my tendency to make less risky choices.
#3 - Is this a good cover to protect the mattress?Amazon.com
You can read more about the different types of mattress protectors and the pros and cons of each in post #89 here. The Luna is one of the thin membrane types that would have little effect on the feel of the mattress and is waterproof but they may also sleep a little warmer than a more breathable protector for some people. If you are OK with this then it would make a good choice yes and this type of protector is quite popular with both memory foam and latex mattresses.
Phoenix