Oh Amber,
Trust those maternal instincts! Your son is going to want access to a stroller during your Walt Disney World vacation in March. How do I know? My husband and I debated endlessly over strollers before we took our son for his first trip to the Walt Disney World Resort when he was five years old. Our son was tall for his age and hadn't used a stroller in nearly a year at that point. However, I suspected that all the walking would wear him out and he might be looking for a place to rest between attractions. I was right! (I remind my husband of that frequently.)
Fortunately, there are places near the entrance of each Walt Disney World theme park where you can
rent a stroller. However, you may want to consider bringing your own inexpensive umbrella stroller with you. That way you have access to that stroller at the end of the day when you leave the theme park and make your way back to your hotel. A sleeping five-year-old can be very heavy. You'll be glad you have that stroller at your disposal once you leave the park.
Whatever you decide about your stroller, have a magical time in March. Bring an autograph book for your son and take time for him to interact with as many of the Disney characters as you can. Those photos are going to be so valuable to you some day. My boy is getting ready to head off to college this fall and I can't tell you how much I cherish those photos from his first trip to the Walt Disney World Resort.
Wishing you many magical memories,
Jill