How Can Future Pregnancies Be Best Prevented?

Hi, this padma (age-30,weight 57,height 152cm) from tamilnadu. after birth of my baby, i was using copper -t for two years. due to the severe stomach pain i removed my copper t. now i am on other loop ( foreign loop said by the doctor- i dont know its name) at last 10 months. over bleeding is a main problem in my periods. normally my periods takes only 3 days. but after insert the loops it takes 5 to 8 days.i take some pills suggest by my doctor. now my son is 4 years old. we decided, one child is enough for us. may i use the copper t or loops for a long last. what is the permanent way to prevent the pregnancy or suggest me any other ideas.( we 100 percent sure of our decision)