Hi Meegs,
Latex and memory foam are completely different materials with very different properties so there really isn’t any way to make meaningful comparisons between them outside of perhaps some very general comparisons in terms of their overall firmness which would be very subjective.
There is more about the many differences between latex and memory foam and how they compare in post #2 here.
I would also keep in mind that different people can have very different perceptions of firmness and softness compared to others and a mattress that is firm for one can feel like “medium” for someone else or even “soft” for someone else depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. This is all relative and is as much an art as a science. This is particularly true with memory foam because the firmness of a memory foam mattress can vary with temperature, humidity, and the length of time it is compressed. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress compared to other mattresses they have tried (see post #15 here). What this all boils down to is that even people that have have tried both mattresses in person in side by side comparisons may have very different opinions about how they compare in terms of firmness.
There is also more about the different ways to choose a mattress (either locally or online) that is the most suitable “match” for your specific needs and preferences (or to another mattress) and how to identify and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them in post #2 here.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs to different body types, sleeping positions, and preferences (or even to other mattresses that they are familiar with) than anyone else.
Phoenix