Introducing bottle feeds to EBF baby

Any advice on how to introduction a bottle to an exclusively breast fed baby ? My son is 13 weeks old and we worked really hard to establish breastfeeding in his first few weeks and once we had we stopped using a bottle (probably a mistake). I have to return to work in a few months so we are working on getting him back onto a bottle but aren't having much luck. So far we've tried different bottle types and teats but he doesn't seem that interested and has only really sucked once so any tips or advice would be appreciated! How long should it take for us to be able to get him feeding from both bottle and breast?