What is a good hair curler to buy?

The safest and healthiest way to go since you already have some nice waves, is plastic curlers. They've been used for over 5 decades, in the fashion & hair industry. Shampoo, towel dry, blow dry halfway, set them in plastic curlers, blow dry, take them out, finger comb (you have some curls already) or brush to style. When your hair is nicely curled, adding heating tools (like straightening or hot rods) can weaken the hair and they break easily. It also causes them to split or not grow normally. If your hair is thin, it will only get weaker & thinner, some resulting in hair falls. So treat your hair with extra TLCs. None is better than the other, no matter what brand, what price THEY ALL DAMAGE the hair. Even if you use hair protectant, it doesn't protect your hair 100%. Like sunscreen, you still get sunburned. Same with hair.