Sensus is just one of many different types of memory foams that are in the 5 lb range. It’s made by Foamex/FXI and almost every memory foam manufacturer both in North America and overseas in Europe and Asia would make a version (or several versions) of memory foam with a similar density alon with higher and lower densities as well. All of these may have a very different “feel” and performance that has nothing to do with density. The post I linked in the previous reply talks in much more detail how various different chemical formulations that produce a similar density of memory foam can be very different in their properties and how they “feel” and perform.
Up to the 5 lb range or so … density has more to do with durability than anything else but past this point (into the 7 and 8 lb memory foams that are made by various manufacturers) the increasingly greater durability that comes with higher density memory foams begins to diminish.
There is a common belief that the most suitable mattress or layering can be “deduced” by height, weight, and sleeping position statistics and information alone but unfortunately there is no “formula” that can do this and personal testing and experience on a mattress is the only way to know for sure what someone will do well with. There are some generic guidelines (in the mattresses section of the site) that can be useful guidelines for different body types, different sleeping positions, and different types of layering that will affect both of these and can give some ideas of the variables involved based on “averages” for larger groups of people but every individual may be outside of any of these averages in one way or another. These guidelines are meant more to give you some basic knowledge which can help you work more effectively with the retailers or manufacturers you are dealing with. It’s also important to remember as well that every layer of a mattress or sleeping system will have some effect on every other layer in a mattress (to larger or smaller degrees) so identifying the characteristics of a single layer without taking into account what is both over and under it can lead to some surprises.
It’s wise to have more detailed conversations on the phone (when you are dealing with online retailers or manufacturers) or in person (when you are dealing locally) because they only have their own mattresses to choose between (or materials in the case of toppers or individual layers). This greatly reduces the options to choose between from a near infinite amount of “theoretical” combinations to just the ones that they have available so they can often make suggestions for which of the more limited options they offer have the greatest odds of being suitable “on average”. The more local testing you have done on materials and mattresses where you know the details of the layers you are testing … the more you can help them to help you make meaningful comparisons and choices. Without this … you are working with “averages” which may not always be suitable for a specific person. The better retailers and manufacturers will be very familiar with how the specific types of materials they offer compare to the more common choices that are available in the larger market in terms of things like response time, softness/firmness, density, temperature sensitivity, ventilation etc. of the memory foams or other types of materials they carry. Dealing with knowledgeable and experienced people along with personal testing can greatly reduce the risk of “mistakes” when you are choosing a mattress or topper materials. More simple layering patterns are much easier to “approximate” than more complex layering choices.
For example for your body type (fairly light and curvy) and sleeping positions (side stomach) you would typically need a thicker and softer comfort layer than many people who were heavier or less curvy but this is partly offset by the fact that you also spend time on your stomach which is a flatter sleeping position and needs a thinner and firmer comfort layer to lower the risk of alignment issues from “hammocking” for this more “risky” position. Some people are also more flexible or have less specific preferences so may have a wider range of designs that can work well for them (these are the people who can sleep on “anything). Others may be less flexible or have a more specific set of needs and preferences that means that there are much fewer types of designs that will work well for them (these are the “princess and the pea” end of the sale) . There are also many differences between people in terms of their physical condition, age, muscle tone, what they are used to (and their body has adapted to over the years), cultural preferences, and natural variations in physical makeup that can mean that even people who seem to be similar may need or prefer very different mattresses or topper combinations. Your experience also indicates that 4” of memory foam … even higher density … is too thick for you (and would be too thick for a memory foam topper “on average” in most cases as well) and that thinner layers or memory foam either by themselves or in combination with slightly firmer and more supportive and resilient “transition” layers underneath would have much better odds of being more suitable for you.
When you are a combination sleeper … then the thinnest and firmest possible comfort layer that still provides good pressure relief on your side with no “room to spare” in terms of thickness is also the least risky in terms of alignment when you sleep on your stomach.
Because of all the variables involved … good local testing along with the knowledge and experience of the person you are working with (either locally or online) is the biggest key to success in choosing either a mattress or topper combinations. They already know what you would otherwise need to learn about specs, materials, and the effect of different designs and you know what they can’t know for certain which is your personal experience on various mattresses and material combinations (including the condition of the mattress you are sleeping on and wat to “fine tune”) and how closely you may fit inside any of the “averages” for people of your body type, sleeping positions, and personal preferences.