Hi, Amanda!
You would be just fine with either your old, sturdy compact digital camera or the new one you're thinking of purchasing as well. In Walt Disney World, every attraction has some sort of compartment where you can stow your gear, even that larger camera. You won't have to worry about it at all as you enjoy the attractions.
Should you wish to lighten your load for a bit, there are lockers available for a nominal fee in each park, near the entrances. You might want to keep your compact digital camera with you and leave that heavier camera in the locker until you're ready to focus (no pun intended...) on photos.
Disney's professional photographers are available throughout the parks as well, ready and willing to take your photo either with your camera or with their own high-quality equipment. You'll be handed a
PhotoPass card which can then be scanned each time a PhotoPass photographer takes your picture, adding these photos to your account. Once you set up your account online, you can view and edit your pics for 30 days. If you plan on purchasing several of those photos, I suggest you take advantage of the
PhotoPass+ preorder discount. You'll save $50 by preordering PhotoPass +, a service which will entitle you to unlimited PhotoPass photos as well as photos from many attractions and dining locations as well.
Send more questions as you think of them, Amanda; we love to help!