A body lift will likely run you quite a bit for labor. I have installed a few body lifts (on other vehicles, but the idea is the same) and they are quite a pain in the ass. Remember, everything that contacts the body and something attached to the frame, will also need to be adjusted/lifted. This includes: body mounts (of course), mechanical levers for t-case and/or tranny, radiator, fuel hoses, steering linkage, etc. (if these apply to your situation). They are not difficult to install, they just take some time. If you can install a suspension lift, then you can do the body lift yourself.
Also, on my trail rig ('97 Jeep TJ), I run a suspension lift and spacers on the front (to level out because of winch weight) and I have had no troubles with the springs sagging. I also have friends that run OME springs on their jeeps and also use spacers (for the same reason I do) and they have no trouble with the springs.