Hi MM2014,
While firmness or softness can be very subjective … carefully testing a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences) can be more objective and is the most reliable way to know whether a mattress is a good match or you outside of actually sleeping on it. For most people, careful and more objective testing on a mattress (hopefully using the testing guidelines in the tutorial post) can do a very good job of predicting your actual sleeping experience but this is different from testing a mattress for a more subjective sense of “comfort” which is much less reliable and can have a lower chance of success than random chance alone (see post #4 here)
This is a very common comment on the forum and it isn’t unusual for people to think this. In most cases it’s because our memory for “feel” or “comfort” isn’t very accurate or long lasting and as I mentioned in my earlier reply this can happen to anyone when there is some time between testing or sleeping on a mattress on different occasions when your frame of reference has changed. Of course it’s always possible that a manufacturer can make a mistake as well.
With your lighter weight and being a side sleeper I would keep in mind that many people would prefer a softer comfort layer than 28 ILD and while a support core of 28 ILD is more “in the range” for lighter body types … many people would do better with a little firmer support core as well. Side sleepers also tend to do better with a little thicker comfort layers although all of this can also depend on the cover and quilting in your mattress and on how the combination of all the layers and components work together because every layer and component in a mattress will affect the feel and performance of every other layer. Once again though … each person is unique and your own testing and experience may indicate that you will do better on a different combination completely.
Phoenix