Engine skid would be #1. Depending on the year of your Jeep will depend on the gas tank skid plates. 03-06 had thicker skids than my rusted falling apart '00 and should be good. The other area you'll want is rocker protection.
Of course this is for rocks so if your swamps don't have rocks and stumps in them, you may be fine. I'd still recommend an engine skid just in case since it's an easy cheap addition.
Why not just go out and wheel and see what will make your experience easier and more enjoyable? We all do that. After my last trip I found that my need is clearance because I still have the stock TC skid. That will be remedied before next summer. You may find that your need is new tires, lockers, whatever.
I agree with blue6tj. Many will say you need to protect the underside first but that depends on what you will be doing.
For most of us that are just doing some trail riding (rough dirt roads) and going through a mudhole now and then, bigger tires would be the best bet. If I come up on something that looks like it would cause my underside to scrub, I just avoid it.