Flexible slats are bad. Avoid them. Higher priced bed frames with flexible slats may work, however in my experience you are just adding an unknown variable to the equation when you buy a base with flexible slats.
The middle of our body is the heaviest. When we lay on flexible slats the mattress “falls in” to the flexed slats beneath it. This can happen in months,, or it can take a few years. It depends on your weight.
It can severely shorten the life span of your mattress, and it can ruin your back. Avoid at all costs.