Hi spindst,
The suggestion is more to avoid more than “about an inch or so” of lower quality or unknown material above the latex because it could become a weak link in the mattress … not to avoid other materials over latex in general which would be more of a preference choice.
Outside of testing a mattress to make sure that it’s a good choice for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences … the most important part of a mattress purchase is making sure you know the type and quality of all the materials in a mattress (see here) so you can identify any potential weak links in the mattress and also make more meaningful comparisons with other similar mattresses. If you can find out all the specifics of the Kluft you are looking at and post them on the forum I’d certainly be happy to make some comments about the quality of the materials or help you identify any potential weak links in the mattress.
You are getting some misinformation here because latex doesn’t come in densities as low as what you are mentioning (see here for some examples of both 100% natural Dunlop and blended Talalay) and they are more likely to be polyfoam densities than latex densities. If you look at the law tag on the mattress you will quickly be able to find out if the mattress includes any polyfoam.
I would also make sure you’ve read the tutorial post here which has all the basic information, steps, and guidelines in one place that will help you make the best possible choices … and know how and why to avoid the worst ones.
Phoenix