Most spring conversion kits will lift the vehicle to stock height; or if you were to run the vehicle to build up air pressure and have the bags up, that's how it'll look. The only downside to springs is you'll feel the ride difference. There's no comparison for air, but for me, air suspension is best left on heavy duty trucks. I prefer air ride, but for my personal vehicles, springs and shocks are best. To best maintain an air ride system it should constantly be under pressure as often as possible, which for passenger vehicles that get parked for a few days at a time here and there, isn't a good thing. A slow leak will also drain the system fully of air allowing the bags to compress to the point where they can crack, even more so if your current suspension is fatigued in any way, as it'll add to the stress that the empty bags have to endure.
Summit Racing - High Performance Car and Truck Parts l 800-230-3030
is a good source for spring conversions and upgrades. I've used and installed helper springs when towing an old RV of mine, it had a tongue weight of 890lbs loaded, which put my Durango on the edge of it's usable payload with the family and gear in there.