Arsene2000,
All you asked for was advice on how to get a good deal on stock size replacement tires (BFG A/T KO). I don't know where you are located, but I looked online for basic pricing. Then I started calling local shops that listed themselves as BFG dealers. Be aware that the online price will not reflect shipping in many cases, nor will it include mounting, balancing, and disposal of your old tires. Also, many shops include free rotation and balancing, as well as road hazard warranty. I had three nails removed and tires repaired for free by my local guy. So, make sure you are comparing apples to apples.
Stock size replacement BFG A/Ts are a good choice for minimum hassle. They worked well for me in all but the snotty, Virginia mud.
Personally, I did not want to change tire size until I could make the speedo/odo correct also. Teaching my kids to drive is enough challenge, an incorrect speedo is ridiculous in that context.
My sig line gives you the information regarding my truck's 200K birthday presents. I highly recommend the Mark's 4WD unit that Christo Slee sells. It is plug and play (plus a little RTV).