Hi jaybackintheday,
While 4 lb memory foam is a good material and is certainly appropriate for more general use … as you can see in the guidelines here, at higher weights I would tend to reduce (and possibly eliminate) the use of 4 lb memory foam for higher weights (regardless of the manufacturer) and would focus on 5 lb density or higher memory foam because 4 lb memory foam won’t be as durable or last as long as higher density memory foam and this would generally be more important with higher weight ranges.
Post #3 here and the posts it links to has more information that would be useful for people in higher weight ranges.
While the choice between latex and memory foam is a preference issue (see post #2 here), latex in firmer ILD’s would certainly be a good option as well and is a very durable material although I would also be cautious with thicker layers of very soft latex at higher weights as well both for durability reasons and because of the risk of alignment issues with a mattress that uses comfort layers that are too thick or soft or support layers that are too soft regardless of the material.
Phoenix