It should be a chelated iron, do not use the oxide form as it is not well absorbed. Floradix is found in health food stores. It's a liquid that is non-constipating, non-nausea producing. It helps to take it with food (to prevent nausea). It helps to take it with 500 mg. vitamin C as it increases the absorption, and also with vitamin A as I mentioned.
The regular dose of iron is 18-20 mg. It should be higher to make up a deficiency, but it's best to have a medical practitioner tell you what dose to take, one who knows your ferritin level and will re-test occasionally to ascertain when you are at the optimal level.
A ferritin below 12 is considered "absent iron stores", below 35 it's considered (diminished iron stores), and the optimal level is around 70-ish. It's not good to have too much either.
Iron comes up real slowly, so it should be taken consistently. To go from "absent" to "optimal" may take a year depending on other factors.
One problem to be aware of, is that if your thyroid is low, you may have low ferritin because your body is not absorbing iron. If so, you may not be absorbing copper either. If your copper is low you can have an iron deficiency anemia that is not cured by taking iron. The body needs about 2.6 mg. of copper/day (or is that mcg?), anyway, it wouldn't hurt to add that in, just in case. It takes about 6mg over a 1-2 month period to make up a deficiency. A quick thyroid test is to take your temperature in the morning before getting out of bed (if you don't have a heated water-bed or electric blanket). Put the thermometer in your mouth for 5 minutes. If the temp reads below 97.6 (98.6 in the daytime), your thyroid may not be functioning very well. That has to be fixed before anything else with work very well.
Here's to a healthy future!