My avatar picture shows me and DS with "our" mei tai. He was older, a bit over a year, but it was SO great to wear him in that most of the day. It was mesh, and I am right now so glad that someone is making mei tais from solarweave! The mesh of mine allowed for us to be MUCH cooler than if we had used a solid fabric one.
Last year when he was a bit over 2, we used the Ergo, which is also fabulous. I didn't get the Ergo until he was 2, so I never really used it as a front-carrier, but I'm sure it would be great.
At 5 months, though I wasn't doing Disney (nor even knowing that we would be), I was still in my pouch and Moby phase, but I think a Moby would be too hot, and even when DS was little I couldn't go very long with a side-carrying pouch. So the meitai and Ergo, IMO, are going to be the best bets.