Hi Diane37,
Unfortunately … if a manufacturer doesn’t provide you with the ILD of their materials then there is usually no way to find out except through your own subjective experience. They really have no reason to provide this information because it’s not a factor in the quality of the material and with a local purchase what your body feels is much more important and relevant than knowing the ILD of the materials (which in most cases would have little meaning or relevance to the large majority of consumers or would be information that they believed was more important than it was).
ILD alone is also only one factor in how a mattress feels or performs and ILD is also not directly comparable between materials. You can read more about trying to “match” one mattress to another in post #9 here and more about some of the other specs that are just as important as ILD in post #2 here. The convoluting in the OMI and the quilting materials and layers will also make a significant difference in how the mattress feels compared to another mattress that uses the same ILD latex.
Having said all that … there is some information in post #8 here about the ILD’s of the Lago (hopefully accurate) that came from a retailer I know but I would keep in mind that ILD is only one factor out of many that are important. I would probably use your experience on the OMI as a rough guideline that points to whether you prefer softer or firmer comfort layers in general and as part of your discussions with FSF rather than use it as a specific “model” to “duplicate”.
There is also more about how to make comfort choices in mattress firmness/comfort levels in post #2 here but outside of personal testing or experience on a mattress … a more detailed conversation with a knowledgeable manufacturer is by far the best way to make your choice because they will know more about the specifics of their mattresses and the options they provide and be in a better position to help “match” you to a design based on the averages of their many customers that are similar to you than anyone else.
Phoenix