Hi QFT,
I’m not sure what you mean by a “slab frame” but a box spring normally wouldn’t be the best choice for either a latex mattress or a latex hybrid mattress (that only has latex in the comfort layers). A suitable foundation would generally be the best choice for either of them. There is more about the types or support systems that are generally the most suitable for different types of mattresses and some sources for each of them in the foundation post here.
There isn’t a way to quantify exactly how long any mattress will last for a particular person and when the gradual loss of comfort and/or support over time leads results in one or both of you no longer sleeping well on it and needing to replace it even if it would still be suitable for the other one or for someone else (see post #2 here). The only meaningful durability comparisons that it’s really possible to make is in comparison to another mattress where you can say “this mattress is likely to be more durable than that one” without attaching a specific number to either one. The Telluride may be a “better than average” choice compared to many other mainstream mattresses in its budget range but could be somewhat “on the edge” in terms of durability (more for you than her) compared to a mattress that used higher quality materials in the upper layers especially. There is more about the many variables that can affect durability and the useful life of a mattress relative to different people in post #4 here but if I was in your shoes it would depend on how the Telluride compared to the other finalists you are considering.
Phoenix