Yes, i think many people  do but the problem is that if the normal mattress has any poly foam, that poly foam will eventually sag and deform and possibly cause pain later (9 months or so....depending).  I think the assumption here is that latex cores will not form permanent sag but provide a firm base for support of upper comfort layers of talalay latex.  The trick would be to get one without poly foam (or much of it) in the top layers.  That mean avoiding pillowtops or even thick foam in many mattresses and would probably mean a very, very firm basic mattress.

See the Higlighted Threads posts at the top of the forum re mattress surgery. I have been using latex over springs for years. See my post about it there along with others. Someone just did mattress surgery  and reported on it last week here in fact.

As to the original post here in this thread, yes, you can just throw layers of latex on top of each other and put anything on top of the latex. THe latex tends not to shift much due to the friction of rubber. I even use zoned pieces cut into thirds so I can have a firmer piece in the middle for my hips and the 3 pieces hardly shift. I check them once a month or so and adjust as needed. Sometimes it's not needed.

I just use a couple of sheets under my bottom sheet for protection of the latex. Is this the best protection? Probably not. But it is probably good enough. Ideally I'd say use a wool layer over your latex, maybe a thick wool blanket or comforter. Sometimes I use a wool layer but mine is too thick (2" or so) and sometimes I feel it causes my lower back to sink in too much and cause pain.