you got sagging coils. I've never experienced it personally, but it's been known to be a common problem.
You got some choices, some are better than others but aren't necessarily cheaper.
1: a spacer. you still have the same characteristics as the spring you now, only the rear sits higher. Bottom out, weak, etc, etc
(personally, I wouldn't do it)
2: stock replacements. If I wanted stock height and a better, less prone to bottoming out coil, this is what I'd do.
3: ever want it lifted? now's the time. In my mind I'd deduct the price of a new or used coil from the cost of a lift coil replacement...then research lifting the front. CAUTION: it will handle extremely different and your CG will of course be higher (more prone to roll) but if you're a driver you'll know when (at least I hope) to get out of it before it does. And you'll be able to get those bigger meats under it.
bigger meats need lower gears. and thus, the cycle starts...