Hi Kate
My DS was exactly the same, only wanted bm from the boobies and no other way!
I returned to work when he was 6 months old and we got around it by giving him 2 feeds of a morning, and 3 in the evenings and lots of water and custards during the day when I wasn't there.
The days I didn't work we continued as normal bf'ing all throughout the day and my supply was fine.
I used to get quite full by the end of the day at work but my supply seemed to even out after a while too.
Hope this helps!