97 chevy 1500 rear springs/lift kit

i have a 97 chevy 1500, 350, duals, 4x4, has a 3 inch body lift and 33x12.5x15's. my rear leaf springs are shot and i'm looking for a good replacement that will also give me some more strength for towing and hauling a trailer. i'm also considering putting a 3 or 4 inch lift kit and was wondering how hard and expensive that might be. let me know your thoughts and experiences soon b/c i'm goign to be hauling a trailer and need to replace the springs soon. thanks.