Just a couple of quick questions about Foamex Sensus toppers..  with 2" of Sensus on an FBM lux-hq slab, would I need a layer of something between them to transition from the firm(!) lux to the soft Sensus? And, how long does Sensus foam last? Or, to rephrase, how many years of use should I expect to get out of it?

Thanks,
Jim