Hi ddt972,
I would be very cautious about using many of the mainstream manufacturers as a way to test latex unless you know exactly what is inside the mattress you are testing because many if not most of the mattresses that they will call latex mattresses or hybrids may only have a relatively thin layer of latex buried somewhere in the mix of comfort layers or may have relatively thick layers of polyfoam on top of the latex so they may not be representative of what latex “feels like”.
You can see the quality/durability guidelines I would suggest in post #4 here. In most cases the support core of a mattress wouldn’t be a weak link and for most people a 1.5 lb base foam would be fine with a high quality and durable comfort layer (such as latex) in an appropriate thickness on top of it but if you are in a higher weight range (above the lower 200’s or so) where you would compress the deeper support layers more than someone that was lighter then it would be worth considering either thicker comfort layers of latex or a higher density base foam (or both) although of course the cost would increase. There is also more detailed information about the many factors that can affect the durability and useful life of a mattress relative to the person sleeping on it in post #4 here and the posts it links to.
While there is no way to quantify how long any mattress will last for any particular person … if you are well inside the comfort/support range that is suitable for you and a mattress isn’t close to the edge of the range that is too soft for you when it is new (see post #2 here) and meets the minimum quality specs that are suggested in the guidelines then it would be reasonable for most people to expect a useful lifetime in the range of 7 - 10 years and with higher quality materials (in the comfort layers especially) it would likely be in the higher end of the range or sometimes longer.
It’s always more realistic to think of 10 years as a maximum reasonable expectation for any mattress no matter what the quality of the materials and then treat any additional time after that as “bonus time” because after about 10 years the limiting factor in the useful life of a mattress will often be the changing needs and preferences of the people sleeping on the mattress and even if a mattress is still in good condition after a decade … a mattress that was suitable for you 10 years earlier may not be the best “match” any longer and may need to be replaced. With higher quality materials throughout a mattress or for people whose needs and preferences or physical condition hasn’t changed much over 10 years then “bonus time” or even “extended bonus time” with higher quality/density materials is much more likely than with materials that are in a lower quality/density range.
Phoenix