Integrated Shoulder Belts, front and back?

Thanks all. My projects for this year, being that the car is new to me as of Jan., are to address anything safety-wise I can think of. Because I want this to be the family summer cruiser, good seating is high on my list.

In addition to convertibles, I thought about looking to see if a modern small hatchback rear seat met the needs and size. Something like a Mazda 3, though I don't remember those being integrated seat belts.