Hello,
I would like to know if it’s incorrect to use a Memory Foam (Visco) layer over a Latex layer?
At the store, the seller told me this is incorrect, since the Latex is breathable and putting the Memory Visco layer over it, would block the breathing of the Latex.
The seller told me to use only Latex over the Springs, or in alternative use only Memory Visco over the srpings.
Is this correct?
Hey mega-biscoito,
Welcome to The Mattress Underground 
! Thanks for stopping by and for your question.
That depends on what you’re trying to accomplish with the feel of the mattress. If you are a hot-natured person, using a memory foam layer over a latex layer would remove the benefits of latex’s natural air circulating properties. If you don’t like the bounce/ lively feel of latex and prefer the “sink” of memory foam, than you’re good to use a memory foam layer to dampen the latex’s more lively feel and still benefit from its’ support factor. Whether you go with memory foam over latex + coils, latex + coils, or memory foam + coils, the choice is more dependent on what your comfort and support feel goals are. The materials are polar opposites of one another in terms of comfort layer performance and feel, but what you propose is not unheard of. However, if your goal is to have the coolest sleep possible, latex over pocketed coils is the better way to go.
Hope this helps and good luck 
!
Sensei