Hi bgaviator,
The length of time that a mattress will last for any particular person depends on many variables so there really isn’t any way to know how long any particular person will sleep well on a mattress before they cross the thresholds to just “sleeping OK” to “tolerating a mattress” to finally deciding to replace it. There is more about all the variables that can affect durability and the useful life of a mattress relative to each person in post #4 here.
Some of the variables include how close you are to the edge of the softness/firmness range of a mattress that would be suitable for you to sleep on (see post #2 here), the quality and durability of the materials in the mattress, your body type, and how sensitive you are to the effects of foam softening and breakdown. A mattress that lasts one person for only months may last someone else for years even if they have a similar body type.
Having said that … post #3 here and the posts it links to has some guidelines that may be helpful for those that are in higher weight ranges. While the mattress you are considering would be a great quality/value choice for most people … I think that it would be a risky choice for you because it is so soft and because the density of the materials may not be the most durable choice for your body type.
Phoenix