Speedy, some questions for you :
1) How long have you been kiting for?
2) How long have you been buggying for?
3) Is it buggy freestyle or buggy racing you want to get in to?
Im guessing freestyle since your asking about buggy jumping......
I personally would not recommend a newbie to use a harness, the problems with a harness is that if it goes wrong and you get face planted there is a high risk of the hook or roller getting caught in the sand / grass meaning that you cant get unhooked from the kite, the safest thing to do is learn to fly the kite in most conditions to a level where you hardly need to look at the kite. Once you are really comfortable about flying the kite then think about a harness.
Other kites that will give you lift are the Ozone Frenzys (which I use in the buggy) or Flexifoil Sabre, these are both depowerable kites which use a bar. There are other kites with plenty lift but until I know how much flying you have done I will wait
What keeps us in the the buggy, as ped said, we use seatbelts (not recommended for newbies) and we also use foot straps, so basically, if anything goes wrong i.e. bad landing and you tip the buggy over, you are still attached. You then have to pull the quick release on the seatbelt and if you are still having problems, pull the QR on your harness system like Kitehighland was talking about.
Wild Beam : Maybe worth searching the buggy section, Im sure there was a large thread about captive systems in there....
CLICK HERE
For buggy jumping info there is a large thread
Here
I wouldnt advice anyone to buggy jump alone, its just too risky!
O.