What size tires will fit my truck? Mine are dry rotten, uh oh

So yesterday I was going to take the 98 Taco in for an oil change and tire rotation and I noticed something. Around the rim, there is some dry rot on the tires on the rubber immediately around the rim. I didn't see anymore. I've got to get some tires. I might be better off buying the rims/ tires off of Craigslist. I have 6 lugs and currently have 265/75R15 that was on the truck when I bought it. What is the biggest I can go with as far as tire and rim are concerned? I've seen some new tires rims off of new trucks very reasonably priced. Any suggestions?

Thank you very much.

 

I'm putting on some 32x11.5x15 BFG K02 tomorrow... I have a 2.5 inch lift

 

31X10.5 will do ya good.