Hi tim408,
I can’t know for certain of course because I can’t feel what you feel or see you sleeping on the mattress but it’s certainly possible that you have “jumped over” an ideal configuration by changing both the comfort and support layers at the same time and that your mattress is now a little too firm. This is especially challenging if you sleep on your stomach in combination with other sleeping positions because as you likely know stomach sleeping is a much more risky sleeping position and a mattress that is firm enough for stomach sleeping can be too firm for your other sleeping positions. This can be especially true for those that are more sensitive to smaller differences in a mattress.
While it’s more common that lower back issues are the result of a mattress that is too soft … it can also be true that a mattress that is too firm and doesn’t fill in the gaps in your sleeping profile can result in alignment issues and the symptoms that come from them. Lower back pain that is there in the morning but then goes away after you are up for a while and your body stretches and loosens up can often be the result of alignment issues over the course of the night but lower back pain that lasts all day can also be from other issues as well so it’s difficult to know what the cause of your pain may be. With 3" of latex that are 24, 24, and 32 ILD over a pocket coil it’s less likely at your weight that you won’t be sinking into the mattress enough but it’s certainly a possibility. It’s also possible that it’s still too soft. It can take some detective and trial and error to identify what may be happening but there is more about some of the more common symptoms on a mattress and some of the possible causes behind them in post #2 here and the posts it links to that may be helpful.
If the cause of your issue is that the mattress comfort layers are too thin or firm then a topper will add some extra thickness/softness and what I call “secondary support” under the small of your back which can certainly be helpful and it will also add some additional pressure relief but with your stomach sleeping I would be cautious to add as little as possible to minimize the risk of alignment issues on your stomach. If you decide that you need or want to try some extra thickness/softness then post #2 here and the topper guidelines it links to will also be helpful.
I would also suggest a more detailed conversation on the phone with the manufacturer so you can take advantage of their knowledge and experience with their own mattresses and the materials and components they use because you can cover a lot more ground and “talk through” your situation in more detail in a phone conversation than you can on a forum.
This is certainly a possibility that may be helpful if you like the “feel” of memory foam. When you are uncertain whether a topper will help you then I would also make the return or exchange policy a much more important part of your buying decision so that you can experiment to see if it works for you with little risk outside of time (and of course sleep quality if it doesn’t work).
I would agree with your assessment and comments here because you wouldn’t be changing the thickness of the comfort layers … only the type of material.
This would be a much more “radical” choice and it’s not a direction I would tend to go until I had tried a few different combinations and changes in the comfort layers to see if they are “pointing you” in the direction of the layering that is ideal for you. The choice between an innerspring and a Dunlop latex core is a personal preference but would be more risky at this point because it’s a complete unknown. There is more about the differences between an innerspring core and a latex core in post #2 here. There are people that I respect highly and that could choose to sleep on anything they wanted to that do much better on either one or the other when it comes to a pocket coil vs a latex support layer (in both directions) and only sleep well when they use the support core that they do best with so I wouldn’t tend to assume that one will work better for you than the other. I would tend to work with what you have a little more first and add a little additional thickness in your comfort layers before making these types of larger changes.
Phoenix