You may want to get a wetsuit sooner than later. That's because water conducts heat faster than air. For warm water diving or diving in the tropics, a lightweight 3mm-neoprene wetsuit will work well. There is also a product called a Diveskin, which is much thinner and more flexible. It works as well for warm water dives.
Most dive shops carry a decent selection of wetsuits for women.
You can also find warm water wetsuits at surf shops. As in all equipment, fit is very important. If it is too big, the water will flow right through the suit, providing no protection from the cold. If the wetsuit is too tight it will constrict your movement. Unfortunately trying on wetsuits is exhausting.