Bed platform with siderails and head/footboards?

My king bed needs a platform but we have side rails with edges meant for wooden slats. We have a metal frame in there now that is 75.5in wide and just barely squeezed into place. But last night it failed and we need something with more legs/support. We cant use a boxspring because of the type of bed it is and I would like the bed to be higher up as if it had a box spring. I see a lot of platforms on Amazon that would achieve the height and support im looking for, however they all seem to measure 75.6in wide with the legs at the outer most spaces of the platform. So my question is basically how do I get a platform into the bed frame? Is there a specific platform made for this exact situation? Do I need to modify my side rails? Am I limited to only being able to buy wooden slats that I would drill into my side rails? I cannot be the first person to run into this situation.