It sounds like you need to do the bottle at night whether or not it aids in longer stretches due to your upcoming work situation. And you'd want to start that a bit before you begin working so that you can rest assured your baby will go to sleep well fed in your absence.
I don't understand why a bottle would help a baby sleep longer though. I understand why it would/could if it was formula, but why does it make a difference where the BM comes from?
And I know this isn't what you want to hear, but I think 4-5 hour stretches followed by two hour stretches is great (and not just because we have it worse) but because your baby is 12 something lbs! Ours is hefty 16 lbs and still never (other than two nights ago with the miracle night... which could be because she slept very very little the day/night before on our 12 hr drive to my parents) sleeps longer than 4-5 hours followed by 2 hr spurts until morning... on a good night! I think, despite how it sometimes feels on here, that that is incredibly normal for a 3ish mo old babe.
But I for real hear you on the loosing it bit.