When people suggest you let him go naked, they don't mean from head to toe. What they are suggesting is sort of a radical (but effective) approach to potty-training and that is throwing out all of your diapers and refusing to buy any more. That's it. Cold turkey. Let him know that he's a big boy now and doesn't need diapers. Get him some extremely cool big boy underwear and have him call the grandparents to brag about it.
There will be accidents. Many of them...which is why he'll probably end up not wearing anything from his belly-button down while you're at home because there's only so much laundry that you can accumulate. But after several days to a week of this, you should see some big improvements. Ideally, he'll be fully trained.
He's obviously ready, there's no doubt about it. But I think we're so scared nowadays becuase all of the "experts" say you'll set your child back if you push that, well, we don't even lightly shove. Not even when it's really needed. Don't go crazy and start disciplining him for every accident. But there is NOTHING wrong with being firm and no-nonsense about the whole thing and expecting him to make the effort.
Whatever you do, do NOT start buying pull-ups. To make this work, this change (from diapers to underwear) has to be significant. Pull-ups are too much like diapers and too much like underwear, which only ends up confusing kids. Nearly every parent I know that's had potty-training issues have been able to track them back to the pull-ups.
For extra tips, I highly suggest you use this site's search feature to look up "potty training" advice from MANY mothers past. :-)