Well it was less effort, took less time and wasn't painful in my experience so it doesn't have to be a great deal better in the health stakes if I followed your reasoning!
Yes, the cost/benefit will be highly individual, which is important to remember.
In a scenario such as this in which the benefit is fixed, the way to drive uptake is either to articulate the benefits better (NB not more loudly) and accept that it still may not shift the balance, or reduce the cost as far as possible.
In this scenario, I'd put the bulk of my money and effort into reducing the cost if the desired outcome is increased breastfeeding rates to six months.
That includes physical and social costs.