Hi 901-Memphis,
I can’t speak to how any mattress would “feel” to you or whether it would be a good match in terms of comfort, firmness, or PPP but I would agree that the 5 lb memory foam would be a more suitable choice for higher weight ranges in terms of durability (even though it is less common than mattresses that use lower quality/density materials). I would add a “slight” caution because of the 1.8 lb density polyfoam base layer but the deeper layers will have less effect on the durability and useful life of the mattress than the comfort layers that are above it.
While latex in general would normally be more durable than even 5 lb memory foam (assuming that the latex is in a suitable firmness range and isn’t too soft for you because softer layers of any type of material will be less durable than firmer layers of the same material) … the choice between latex and memory foam is more of a preference and budget choice than a “better/worse” choice.
Memory foam and latex are very different materials with very different properties that are more opposite than similar (memory foam has little to no resilience, has a slower response, and is temperature sensitive while latex is a highly resilient, faster responding, and non temperature sensitive material for example). There is more about the pros and cons of memory foam vs latex in post #2 here but the best way to know which type of materials you tend to prefer is based on testing a range of mattress in different firmness levels in each category to see if you can identify any “pattern” in your preferences.
Phoenix