Hi rellwood,
I can’t tell what is in your mattress from the specs you gave me (there is only generic information) but if your mattress is still in good condition and hasn’t softened and all you need is some extra pressure relief then a topper can be a good idea. Post #8 here has some guidelines you can use to help you decide which may be best. Post #4 here has links to some of the best sources for toppers that I’m aware of.
The choice between latex and memory foam is a matter of personal preference and if you prefer a more “in the mattress” feeling, less resilient, and more “movement restricting” material then memory foam is the way to go and if you prefer a more “on the mattress” feeling and a more resilient and movement friendly sleeping surface then latex would be the way to go. Latex is generally cooler than menory foam as well. It’s usually a good idea to do some local testing on a material you’re not familiar with if you are considering using it as a topper because your own preferences are the most important factor. Both can be very pressure relieving.
OK … now this makes sense. It’s called the Seven Comforts. It’s not available on Amazon at the moment and you can only get it in King size on their own site.
Edit: see post #52 here if you are considering ordering this topper.
So back to this …
While I don’t give specific suggestions based on “theory at a distance” … I can help you with how to choose and help you connect with people who are more knowledgeable and with a more detailed phone conversation can help you make good choices. I would first make sure that you like the “feel” of latex by testing it locally and if you do then a latex topper could certainly be a good choice or even two (one solid and one shredded). Latex is more durable than memory foam but 5 lb memory foam is also a very durable material. I would tend to buy one topper at a time and then buy a second one if it was necessary based on your experience with the first. One variable at a time is much easier to deal with.
My only “concern” is that for a couple of years it seems you were reasonably happy with a 2" low density memory foam topper and I don’t know what is in the top of your mattress (the list was off the law tag which only has generic information) so I would tend to stay with 3" or less so you would have less risk for alignment issues.
With your heavier weight you would be 'safer" going a little thicker than people who were lighter so for you a good 'average" suggestion would probably be in the range of 3".
Phoenix