[Perfectlap]

I went through that on my old Miata once. Installed a sport set of Tokico's shocks and springs. Man it was no improvement. Turns out the spring rates were too light and it was causing the car to bottom. I installed a set of KYB adjustables and a different set of springs from a Miata aftermarket company. Even though the car actually sat lower, the heavier spring rate kept the car in place way better over the bumps. I also installed rear shock mounts that allowed the rear shocks to have more room to travel without raising the car. What a difference. Night and day. All the pluses of a low profile stance without overly sacrificing the comfort.
Why did I sell that car!!!!??? The beauty of it was that all parts barely cost a grand.

If you plan on keeping that 99 for a while you might want to look at coil overs.
You can adjust the rebound and travel so that its actually a notch or two softer tha factory. I think I saw a sale somewhere for $1600 Billstein PSS9's. Not cheap when you factor in labor. Suspensions are tricky. I think the springs are your culprit. You may need to go to the non-sport.