Our spring wood frames are available from rigid to flexible, with narrow or wide slat spacing. The ventilation is crucial in that decision. Ventilation should be at a minimum of 30%, i.e. the slats should allow a free space of 30%. The rule of thumb is: The thinner the mattress, the more flexible the base suspension needs to be, because it needs to effect the greatest part of the ergonomic bedding. In this case, it would be reasonable to select a smaller slat spacing. On the other hand: The stronger the mattress, the greater the slat spacing can be.