There are umpteen different ways to approach this, obviously, but I have to say I’m a big fan of the ‘jump in at the deep end’ method :). My daughter is now three and a half and she has been dry throughout the day (and mostly at night) for more than 6 months now.
We deliberately waited until she showed signs of interest - I know my daughter and there’s no way we could get her to do ths until she decided to. It’s great that your little guy is keen to use the potty, of course. We also made liberal use of stickers and treats to bribe her to give it all a try. We had most difficulty transitioning from the potty-as-novelty phase to the this-is-normal-now phase.
I hear what you’re saying about the mess associated with going straight to underwear but honestly, that’s’ the way I’d do it. After a couple of weeks of introduction, we just said to our daughter ‘right, you’re not a baby any more, so you don’t need nappies in the daytime, do you? Isn’t this great?’ Yes, it was a bit messy, but we made sure that the first couple of days were quiet and home-based so that we could change her regularly. We also put her on the potty very regularly those couple of days to try to catch any accidents before they happened. It didn’t always work, of course!
One of the things that I’ve read which makes intuitive sense to me is that modern nappies are so successfully absorbent that toddlers just aren’t used to feeling damp on their skin, so they’re disconnected from the effects of the process as it were. So, I feel it’s an important stage for them to feel what happens when they wet, so they become attuned to what happens. Having said that, you don’t want them to have to sit around in the damp for long so that’s another advantage to having a couple of home days during that phase. One of the key things, I think, is that once you’ve made a decision to stop with nappies in the daytime, for instance, you really have to stick with it and not go back to the easy way unless you really really have to for some reason - it’s going to send mixed messages.
It’s really important to my daughter not to be labelled as a baby, and we traded on this without mercy. She chose her own underwear, which are for every described as ‘big girl pants’ in our house, and actually she abandoned the potty very quickly for a toddler seat on the main toilet. We have a strange step-stool arrangement which means that now she can actually do most of the process of going to the toilet by herself, which she loves.
We deliberately avoid pull-ups on the grounds that we wanted her to make a distinction between nappies, which she could wee in, and pants which she shouldn’t. Some of my friends take my attitude, some make use of them happily. What we did find was something called trainer pants. These are normal underwear shaped, but slightly waterproofed and lined with towellling, so they allow for slightly more confidence when out and about, but are almost the transition between nappies and pants in a similar way to pull-ups. They weren’t useful for long, but they were very useful for a time (isn’t that the way with all baby equipment?).
Leaving the bad news to last, although YMM and hopefully Will V - after this length of time, my daughter is only just willing to try pooping in the potty. Until the last couple of weeks she would deliberately wait until her nappy was on at night, or previously for daytime naps, before pooping. Now we’ve stopped nappies during any naps she has, she has (grudgingly) agreed to use the potty if she needs to poop during the day. She’s still not keen, although when we talk it through she agrees it’s the right thing to do.