Nipple shield

Ok I'm having a baby in 4 weeks and having a c-section I have looked at them online but haven't really looked personally any way I seen they have 20mm and 24mm any other pregnant women or moments on here used these I have such a hard time with getting my milk supply up after having a c-section but really wanna breast feed right away I no it is time consuming after a c-section but I'm just wanting other opinions thanks in advance to whoever comments