I go commando everyday. Only time I've had chaffing is when too much sweat got down the front side as well. If I'm sweating a lot, I try to rinse in a creek as able to wash the salts, etc. away.

Don't think that would work for my son who has fatter legs. The Starter compression shorts at Walmart ($10) are the cheapest I know of. Get a size too big so they aren't too snug over time.

I would think anything really loose like running shorts wouldn't solve the problem.