It's not the slats. They're nearly 1 inch thick tropical hardwood. I can stand on them easily with little or no flex. The problem is that the mattress is just piece of yellow foam. However, I had the same problem with my last two mattresses in the US, which were inner spring mattresses with a box spring and metal frame. They were probably sagging at least 1.5 in" on my side and 3/4" on my wife's side with a hump in the middle. Then after flipping them, they sagged on both sides.