Hi jt408,
Diamond mattress is a regional manufacturer which is doing things right IMO. They are making high quality mattresses at a good price and I would choose them over a better known national brand every time. I have also been told they are also very responsive to their dealers and are open and transparent about the materials in their mattress with their dealers (although this may not always be the case as you can see in post #2 here). There is no doubt in my mind that they would generally have better quality and value than mainstream brands and the two models you mentioned will likely have better durability than the iComfort Revolution. You would do well to switch if you need or choose to IMO.
The Natural uses a higher quality polyfoam (what they call eco-flex) which uses some plant oils to replace some of the petrochemicals usually used in the manufacture of polyfoam (thus the “eco” name which is a bit of greenwashing which the entire foam industry is promoting at the moment). Used in the support core of a mattress … this is a durable material and a good choice for those who want the benefits of a latex comfort layer but don’t want the expense of a high quality latex support core underneath this. Memory foam of any type is too soft to be used in the support layers of a mattress which is why it is only used in the upper layers.
The hybrid line uses a pocket coil spring which is also a good choice which is also less expensive than a latex core. There are many who prefer the feel of an innerspring mattress over a foam core and which one is chosen would be more a matter of preference than “better or worse”. While a pocket coil is the most motion isolating and conforming choice of the innersprings … a polyfoam core will do both just as well (particularly with latex over them which is almost as motion isolating as memory foam).
The two basic functions of a mattress are pressure relief (the primary role of the upper layers called the comfort layer) and spinal alignment (the primary role of the lower layers called the support core). Each of these should be tested separately. The comfort layer should be thick and soft enough to form a pressure relieving cradle to distribute weight and relieve pressure. The support core needs to be firm enough to hold up your heavier parts … in particular your hips. Side sleepers typically need a thicker softer comfort layer than back sleepers while stomach sleepers need the thinnest firmest comfort layer of all. This is why a mattress can be both firm (on the bottom for support) and soft (on the top for pressure relief) at the same time. After these two priorities … everything else is preference (such as sleeping more “in” your mattress rather than “on” your mattress … the feeling of innersprings over polyfoam in the support core … sleeping temperatures … and other subjective choices).
If you were heavier … I would probably tend to advise that a high quality and firmer polyfoam core would be more suitable but you are light enough that I would make the choice based on your and your wife’s preference.
As long as you are testing for pressure relief (5-10 minutes completely relaxed on the mattress on your side testing for pressure on your hips and shoulders if you sleep in this position) and then separately testing for spinal alignment in all your sleeping positions (making sure your shoulders are sinking in far enough on your side and that your hips aren’t sinking in too far in any of your sleeping positions), then you will likely make a good choice. After that make your choices based on preference and value.
Good luck … and my “vote” would be for one of the Diamonds but of course it’s always important to make sure you know all the details of the layers inside any mattress you are considering so you can make an informed choice 
Phoenix