It is clear that you need to stay away from iron. You need to be sure that the brand you take is free of iron. Therefore, I would recommend that you use a brand that has a pharmaceutical level of quality control (e.g.. Wampole). The health care provider or pharmacist should be able to obtain the certificate of analysis from the manufacturer.
In addition, often vitamins for kids are iron free (e.g., Wampole Multi-Vitamin for kids is iron free). This is a requirement of Health Canada for kids. Your health care provider should be able to tell you how many to take for an adult dosage.