What do I wear to keep me warmer while swimming?

It is a heated pool, not a lake, so I don’t need mega protection from the water temperature. When I do water aerobics I am not warm enough, and last week my fingers were blue by the time the class was over. I saw swim shirts at the store for sun protection, will they keep me warmer also? And, do those shirts go over a bathing suit, or instead of a bathing top?