I suspect with smaller cars, there will be lap belts only. But you can get some sort of contraption that adds a harness to the lapbelt and anchors it to the car in the back, don't have the link at hand but have seen it and a couple of places in Auckland that will install it.
Apart from that, I'd love a Polo. I had similar requirements to yours and ended up with a Mazda Demio, which fulfills our needs. I just drive it around town, and it's fine for that. However, it's the kind of car that has no character at all, and since it is silver, I can't even spot it easily on a car park... In the first two weeks, I had two people drive into me, so it really is very unnoticable.
With a slightly bigger budget, I would have gone for the Polo...
Good luck with your search,
Daniela