I have a nearly 4 yr old who typically likes to walk and a 5 month baby. We are going to disney soon and I occassionally need a seat for my older ds at the mall or something. It seems silly to drive around w/ a double stroller in my trunk when I normally need a single. So, I'm torn. Should I buy a double? a sit and stand? or just bring two seperate strollers to Disney? On buses and monorails what would you think is easiest?

I have a bad back so I do not want anything too heavy.