Might help to find out what is causing the 'wishy washy' sensation. It might not be anything to do with the suspension.

Nail down what is wrong and then attack it rather than flail(c) and chuck parts at it.

Also, after talking to many more knowledgeable people than me on coilovers it seems that they are rather extreme and will kill the normal ride.

Also its a diesel for gawds sake, why is he thinking of coilovers. Get a set of decent uprated shocks and go with that.