The second comment down said that higher quality slats than Ikea used are $4 each. Ikea level quality is $2 each. I had an Ikea couch once with slats like that. A couple of them broke from people kneeling on the couch or whatever.  We lived 400km from the nearest lumber store so I just replaced the whole trashy thing with a sheet of more readily available plywood. Everybody in town lived on furniture made of 2x4s, plywood, and foamies anyway.