Each SleepSafe® Bed needs some type of foundation for the mattress to rest upon. With the Articulated and Hi Lo foundations, the mattress rests directly on the electric frame. With the Fixed foundation, you have a choice between a box spring or bunkie board for your mattress to lie upon. The only difference is that a bunkie board is 2 inches high and a box spring is 8 inches high.
When the goal is to maximize safety rail height above the mattress you will choose a bunkie board so that the mattress surface can be positioned 6 inches lower within the bed’s foundation. When the goal is to raise the mattress surface as far from the floor as possible, then you should choose a box spring so that the mattress will be positioned 6 inches higher. There is no price or comfort difference, only a height difference.