Dress should be appropriate for the season. We advise you to wear the same clothes as for a walk in the countryside or forest, and good shoes (no heels or flip-flops). Pants are preferable to shorts, as we sometimes land in fields with tall grass or nettles, and you may also feel cold after landing if you fly at the end of the day.
It’s not cold on board the gondola. The air in the balloon is heated to enable us to fly. It cancels out the temperature drop associated with altitude. So you’ll have the same temperature in flight as on the ground.