Hiya, I'm in a very similar position - DD is 22.5lbs and nearly three feet. I have a mothercare sling which I'm still using in the inward facing position and it's fine for short journeys. But it's a bugger to put on if you don't have eight arms!
I've worn DD for three hours and I lost a pound in weight that day! My tip would be to take lots of water for both of you too - you get really hot hoofing them around.