welcome
I suggest you add your location to your profile.
Not sure who is keeping killies down there at the moment. If you are joining the Dunedin Aquarium Club then they will be able to help you. They are a friendly bunch and a good mix of experienced, and not so much so.
There are not many killies available in NZ as the NZKA has not been too active lately and some species have been dying out. Hard to get them back in the country once they are gone! They are not often seen in shops either.
It is not so much a case of insulating the tanks, but insulating the room they are in. I have polystyrene under mine but that is because of quakes more than for insulation.