Hi Cfrivera,
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The Luroy would change the feel of the mattress compared to a solid non flexing base so this would contribute to the feel and “springiness” of the mattress that was on top of it but if the combination is a suitable match for you in terms of PPP and the bed you are using (the Malm) also has a center beam with good support to the floor underneath it and if the bed itself is strong enough for the weight of the mattress and the person sleeping on it then it should be fine IMO.
The firmness of a mattress depends on many factors including the thickess of the layers, the ILD of the layers, the type and blend of the latex (which affects the compression modulus of the material or how quickly it becomes firmer as you compress it more deeply) and the type of cover and quilting. There is more about the many variables that can affect the firmness of a material or a mattress in post #4 here but there are so many variables and the perception of firmness/softness is so subjective and relative to the body type, sleeping style, and sensitivity of each person that the only way to know how one mattress compares to another one with any certainty would be based on your own testing or experience.
Having said that … it may be worth talking with Neal at Spindle Mattress who has the Blue Shoal mattress with two 3" layers of latex that also uses Mountaintop latex (except it’s 100% natural instead of the 85% natural in the Morgongava) and if the layers were the same firmness (I believe that the Ikea uses C3 firmness in their mattress … see post #70 here) … the slightly thinner layers and the higher natural latex content may give you the firmer result you are looking for although they may only sell it in a twin size because it’s primarily designed for children or for lighter body weights.
Phoenix