Hi tmac_79
I’m not sure about the density of the memory foam that was in your Restonic but there is no doubt that any materials will not last as long with much heavier than average weights. I would also be very hesitant about using memory foam at all because of how easily it can soften much more quickly … especially with thicker layers. If you did choose to use memory foam … I would be looking at high density options (at least 5 lbs and preferably higher). Some of the models of the King Koil HD series use 6 lb memory foam for example.
Post #2 here and post #2 here also have some useful information about heavier weights that may be helpful in your decision.
In general terms though … the upper layers will have more of an effect on the durability of a mattress than the lower layers (although both are important in terms of finding a mattress that suits you) because they will soften more quickly than the lower layers. Latex will also be more durable than high density polyfoam (HR polyfoam which has a higher density than 2.0 lb HD foam will also be more durable) and in the higher densities tha are normally used for a firm support layer will also be more durable than an innerspring. Bear in mind though that no matter what the material … it will wear faster with heavier weights.
There is no doubt that the King Koil HD mattress and foundation (which is built very strong as well) are much more durable than an “average” mattress. As a matter of fact … some models (such as here) use even higher quality materials than you mentioned (in this case 2.5 lb HR polyfoam and 6 lb memory foam) and some (such as here) use talalay latex as well as part of the layering. 12.5 gauge innersprings are also the strongest gauge innersprings generally available however the gauge of an innerspring in only one of several factors which will determine the suitability of a mattress for your needs.
These same quality of materials are also available though to most local manufacturers and many better sleep shops who sell alternative or local brands and who are also very knowledgeable and can provide excellent advice about the combination of materials that will meet your needs for pressure relief and alignment as well as your preferences for things like durability. They are usually “expert” in helping people with a very wide range of needs and preferences and besides their knowledge about helping to fit" a mattress to different people their value may also be better than larger brands such as Comfort Solutions (King Koil).
So while the King Koil HD lineup uses some high quality materials … it is certainly not your only or perhaps even your best choice in terms of your needs, durability or value. If you let me know the city you live in I’ll be happy to see if I know of any local factory direct manufacturing or better outlets in your area.
Another example of a mattress designed for heavier weights is here. Bear in mind again though that these materials are available to any manufacturer and are not only found in mattresses that are marketed as being for heavier people.
While I understand your hesitancy, memory foam and latex are two very different animals and latex has been around longer than either polyfoam or memory foam and it’s durability has been proven over many decades. You can see some examples of very old latex mattresses here. A high quality latex mattress may not be the lowest cost of your options but it would likely be your most durable choice of all … especially if you buy it from a manufacturer that has exceptional value.
So overall you have many good options but the first step I would take (besides looking at the King Koil HD models that may suit you best) would be a local manufacturer if there are any in your area or some of the better online latex manufacturers such as SleepEz (Savvy Rest is high quality and uses similar materials to some of the SleepEz models but is not in the same value range).
Phoenix