Hi Sujaan,
The choice between a quilted cover and an unquilted cover really boils down to one of preference.
An unquilted stretch knit cover will allow the feeling of softer latex to “come through” more and will allow you to sink into the latex a little more than a quilted layer.
If the cover is quilted … then the quilting would affect and modify the feeling of the latex underneath it depending on the type of quilting that was used.
For example … if the quilting was softer polyfoam … then it would soften the surface feel of the mattress and create a little more “plush” surface. It would also lower the resilience of the surface and provide a more “relaxed” and less “lively” sleeping surface (latex is more resilient than polyfoam) and change the pressure distribution slightly.
If the quilting material is a natural fiber like wool or cotton or a synthetic polyester fiber … then the fibers may be more compressed and firmer than the soft latex underneath it and depending to some degree on the amount and compression of the wool or synthetic fibers and the softness of the latex underneath they can firm up the mattress by slightly lessening how much you sinking into the softer latex or how well it can contour to your body profile. Using wool in the quilting (which is a very breathable and humidity and temperature regulating fiber) can also help in improving the temperature regulation and microclimate of the mattress.
So for someone that wanted the more resilient feel of latex directly on the surface of the mattress … then an unquilted stretch knit cover would be a good choice (this is the type of cover that Pure Latex Bliss uses for example).
For someone that wanted a slightly firmer feel and the benefits of wool … then this type of quilting would be a good choice. The degree that the wool or other fibers affect the comfort layers in the mattress would depend on the amount and compression of the fiber, its quilting pattern, and its firmness compared to the latex or other materials underneath it. Natura for example uses thicker layers of wool in the quilting.
Others like the Ultimate Dreams and many others use a polyfoam quilting which will create a softer surface (the top layer would be softer than the ILD rating of the latex) and this will also lower the surface resilience or what some people call “pushback” feeling of the latex which changes the pressure relieving profile of the mattress (the amount of weight that is supported by different areas of the body).
You will usually see latex with either an unquilted stretch knit covers to allow the "feel of the latex to come through more, a more “natural” or “organic” cover quilted with wool which are a little less stretchy and will increase the firmness slightly vs a cover with no quilting at all (and will create a more breathable and microclimate/temperature controlling mattress), or quilted with softer polyfoam to modify the surface feel and resilience of the latex … but this is all a matter of personal preference and of course budget.
There is more about quilted covers in this article along with Post #6 here (wool quilting) and post #2 here (effects of quilting and different materials and quilting patterns) and post #12 here (brief response about quilting foam).
Phoenix