Based on your criteria the Matrix seems to meet your needs, as it is not as low as the other hatchbacks like the Mazda3, Focus, or Elantra. I agree with johnnygenx, and look for a used one, unless the new ones have cash on the hood.
An alternate could be the Mazda5, very easy to get into, right height, sliding doors nice and convenient, keep the 3rd row down and you will have more space than any hatchback...