Hi. Ds (3.4) is just the same, and we do actually go on naturist holidays sometimes , which has added an interesting dimension to our explaining the rules 'over here'.
I try to be very relaxed about this, getting ds (who is a hot bod anyway) dressed only when necessary. He wears a fresh long-sleeved T-shirt to bed, and will wear it for most of the rest of the next day. If we're at home, that will be just a T-shirt and nothing else. If we're going out in the car, ds will sometimes add the trousers before getting in the car, though he frequently rides naked and we just put his clothes on when we get to our destination - still in the car. And he always wants to cooperate by then.
It does help that ds has developed a bit of normal self-consciousness - he wouldn't now want to be in the supermarket naked, though would prefer to be so at home. So he won't go out/get out of the car without being dressed. Before this kicked in, we explained that it's a rule in our country to be dressed when you're out and about, and that we couldn't get out of the car and do 'x' until he was dressed. Works fine.
Two other tricks: (1) I don't know if your ds is out of nappies, but ds is, and we don't put him in pants, much to grandparents' horror. The primary reason is that he's more likely to use the loo, as it feels less like he's wearing a nappy. But it has the added bonus of less clothing to put on. (2) Don't worry about getting loads of layers on your ds. Just cover up his top and bottom, and then let him come to you if he's cold and needs another layer. This coupled with the commando approach (the French do it!) and the T-shirt from the night before means you have a pair of trousers to put on him and that's about it!
Oh, how's this for another idea: if you're prepared to don some layers yourself, you could turn your heating down/off as the autumn progresses, so that your ds gets a bit nippy and starts to ask to wear clothes?! Although we had central heating at home, Dad rarely turned it on, and so we wouldn't have dreamed of wearing anything less than about five layers!
Oops, long post, but HTH.