Hi karolyn,
Latex and memory foam are very different materials and can’t really be meaningfully compared to each other. It would be like asking which type of apple would be closest to an orange and the only meaningful answer would be “none of them”.
Latex is highly resilient, has a more “on the mattress” feel to it, and responds to pressure. What you feel on latex stays the same over time. You can read more about the pros and cons of latex in this article and more about the different types and blends of latex in post #6 here.
Memory foam on the other hand has very low resilience, has a more “in the mattress” feel to it, and changes its feel and response with pressure, temperature, humidity, and length of time it is subject to compression forces. It can feel firm in some conditions or circumstances and soft under different conditions. You can read more about the pros and cons of memory foam in this article and more about the different formulations of memory foam in post #8 here.
Memory foam is more motion restricting while latex is more resilient and doesn’t restrict free movement on the mattress.
Both are good at motion isolation because they are both very “point elastic” (one area can compress without affecting the area around it) but memory foam is a little better at this.
Latex is more breathable and tends to sleep cooler than memory foam.
Latex also comes in a wider range of firmness levels than memory foam and in firmer versions can be used in the deeper support support layers of a mattress while memory foam is in a softer range and can’t be used in the bottom support layers of a mattress (it needs a firmer material or component underneath it). Latex in general is also a more “supportive” material (gets firmer as you compress it more deeply) than memory foam.
Latex is also a more durable material overall than memory foam although higher density memory foam is also a very durable material.
The only way to really know or appreciate the difference between them is to test both of them in person at local retailers or manufacturers and if you let me know the city or zip where you live I’d be happy to share some of the better retailers or manufacturers I know about in your area where you may be able to test different types of latex. This can give you a reference point about how different types of latex feel to you and how they may compare with different types of memory foam in your own personal experience (which may be different from the next person).
Both can be equally pressure relieving but it’s also important to know that any topper (or top layer) will interact with all the other layers in the mattress you have and the same topper can feel quite different on different mattresses. Your own body type, sleeping style, preferences, and sensitivities to different foam properties will also change what one person feels on a material compared to someone else.
Having said all that … if your mattress is too firm and only needs some extra pressure relief and it has no soft spots or “dips” in it, then a topper can be a good choice to improve the pressure relief and comfort of your mattress and the topper guidelines in post #8 here and the posts it links to along with conversations with a knowledgeable manufacturer or retailer you are considering buying from who can give you specific information about the toppers they sell that you are considering can help you make the best choice for your own personal circumstances
Phoenix