My experience with the various foam mattresses (visco, latex, etc.) is that in order for them to perform to their design, they should be resting on a solid no-yeilding, non-flexing base. Most use matching foundations that are rigid (Tempurpedic for example is super sturdy!) and platform beds are even more sturdy. I will say that if the slats provide some tyupe of zoning for comfort, it is not the right choice for your mattress unless it was designed with that base underneath it in mind... If you get a platform bed with slats your single most effective tool would be to cover a piece of plywood, set it on the slats and place your mattress over it. the caovering of the plywood is toredcue any moisture that may still be in the plywood.. or just sand it, stain it and seal it to create the barrier between your mattress and the smooth foundation.
I will say the biggest down side to using slats only is that foams like to compress into spaces (think about your back, wist, neck, etc.) and will also try to press betwwen the slats they sit on. I actually used the cardboard (2 layers thick) from my Tempurpedic mattress, cut to fit the slatted platform precisely and then set my mattress on that to avoid any spaces for the foam to press through.
Lastly, the height is extremely important (with or without surgery) while sitting on the set (while it is complete) you want your waist to always be higher than your knee(s) so that you are ergonomically in a more comfortable position to get in and out of bed. Get a doggie ramp or steps to make it easier for your friend! He/she will like it if you are as happy as they are!
Most retailers carry a "slat set" that you could place on the Sultan in leiu of the "zoned" slats which would provide the level, non-yielding, non-flexing surface as well.
