Hi sfmom,
That may be a “tough sell” if there is no visible evidence of damage 
There are many different types of memory foam that have different properties and some have a faster response and are less temperature sensitive than others (see post #9 here and post #8 here) and the thickness of the memory foam in a mattress will also have a significant effect on the motion restriction or “stuck in the mattress” feel of a memory foam mattress. Thinner layers of memory foam with more resilient materials either under or over it will still have some of the “memory foam feel” but will tend to be less motion restricting than mattresses that have thicker layers of memory foam in the comfort layers.
Memory foam will also tend to sleep warmer than latex mattresses with wool quilted covers although this would only affect those people who tend to sleep “too warm” on some memory foam mattresses.
As you’ve read … I would be very cautious with 3 lb memory foam as well.
Phoenix