RJ - try either M&S who do a limited range, or an outdoor shop and look for products like Lowe DriFlo, Patagonia Synchilla, or other similar wicking material - most outdoor shops can recommend as nearly all decent hiking vests have moisture wicking properties. Test for softness as well as some can rub the old nips up when sweaty - suggest with your size you should tape the nips up with zinc oxide tape/plasters/Compeed type material before attempting a very long run - seen too many large runners with bleeding nipples. Also vaseline the armpit, crotch and any other possible area where skin rubs on skin as well. And go for lycra shorts to help overcome inner thigh rub - you can always wear a pair of baggier ones over the top if you are little self conscious.
I speak from experience being an ex-lardarse!!