Best bottle nipple for breast fed baby??

Help! I discovered yesterday that my now exclusively breast fed baby won't take to the bottle he used to use when we had to supplement formula (when he was 4 days old). He's now 1 month. My SO tried feeding our son some of my pumped milk last night as I was taking some time for myself and he kept refusing the bottle and crying.

I'm supposed to return to work in about a month and there will be at least 4 hours that I won't be with him. What is the best bottle nipple for breast fed babies??