Do I need to express?

I'm expecting my first and plan to exclusively breastfeed for as long as I can. I'm not sure if I need to express as well, it seems like a lot of extra work (heating bottles, sterilising, etc. Although I've already been given a steriliser and bottle warmer so it won't cost too much). I work from home so I could feasibly breastfeed only, but would this mean I could never be away from baby for more than 2 hours? Is it reasonable to think I could do this for the year or so I might be breastfeeding? The only time I can think this would be an issue is that I go to the cinema once a month and I couldn't take him there (at least I assume its rude to take a baby to a movie). Thoughts?