Girls, hi! It's been almost 5 months since I had my baby. Can you tell…

Girls, hi! It's been almost 5 months since I had my baby. Can you tell me how people protect themselves? Condoms aren't an option for my husband, and I don't feel comfortable with COC pills (I always forget to take them, plus my gynecologist said it's not suitable for me). I'm considering a diaphragm. Has anyone used one? How do you choose one? What should I do beforehand? How does it work? I also heard that after using a diaphragm, people gain weight, is this true? Which type of diaphragm is best? (I read about many different types).