Welcome aboard, Susan! Booking a magical vacation on the Dream is very exciting, but I understand your concern over which stateroom to choose to minimize seasickness.
Though I personally do not suffer from motion sickness, I know many people who do, and they have all agreed that midship is best for them. Some say mid-deck levels too, while others swear by the lower decks, it really just depends on the person.
Take a look at the
Deck Plan for the Disney Dream (click Deck Plan in the photo on that page). If you look at Decks six and seven, you'll see that there are plenty of Family Oceanview Staterooms in the midship section. If I were you, I'd probably go with a stateroom in the midship of Deck six.
The dramamine patches seem to work very well for many people, so you may want to look into that before you set sail. Side effects can be rough though, I understand. Friends of mine said that they felt best if they only wore the patch on rough sea days when it was really necessary, so they lessened the side effect. You'll have to feel it out to see what will be best for you.
If you begin to feel seasick, it is recommended that you stand out on deck (or on your own verandah), close your eyes, and when you open them again, look out at the horizon. This is said to reset your inner ear and help with the seasickness. Also, be sure to stay hydrated, which also helps.
Let me know if you have any other questions as you continue to plan your cruise, Susan! I'm happy to help!