Sorry for bombarding you with links! Hopefully there is something in there you like. I would suggest a mid-length dress, not something too long since you kind of want it to be the same length or shorter than the grad gown they are going to make you wear.
Just wear a nice pair or heels or flats with the dress! Congratulations on graduating!
Luckily, your figure will fit most dresses. I would go with a dress that hits just above the knee in a color that docent look to weird with the color of your gown. Halters are nice and I think a dress that becomes tight at the waist, then becomes looser at the hips would look nice too.