'06 Leaf Spring Replacement

Hey, first time poster on the forum. I have an '06 Access Cab and I'm ready to stiffen up the suspension in the bed. I can't carry a load over 300 pounds without the bed bottoming out when I go over bumps. I surf and ski and find myself driving over crazy terrain fairly often but I don't go off roading specifically.
I'm thinking of doing one of 3 things. First, a simple add a leaf, will this solve my problem and make a noticeable difference in stiffness?
I am also thinking of replacing my leaf packs. My truck has 3 leafs standard, if I upgrade to the 4 spring pack, will this effect my drive train or front suspension?
Finally I'm considering a full suspension upgrade by doing Bilstein 5100's to the front and 4 leaf pack to the back. How much does this cost roughly and is it worth it?
Any suggestions on what to do?
Thanks

 

Welcome to TW & any changes to the stock suspension is a plus, for starters on a budget, theres probably no better fit than to start with 5100's on all corners & A couple Chevy truck springs for the rear, if you're a do-it-yourself guy, easily doable for under $500....