Unlike the advise you may get at some pet shops, sub tropical does not mean coldwater.
Find a proper (tropical) fish shop in you area and ask others about the shop. Beside reducing the likelyhood of bringing home some disease with your fish/plants, they buy from reputable breeders who only breed from good stock.
We have no idea how much you know about fish so why not join up with a
Tropical Fish Forum where you can ask specific questions and get mostly intelligent answers.