Baby still won't fall asleep without the boob

Hey guys my son Is coming up 9 months next week. The past month he has finally taken to a bottle so he is now mixed fed but still prefers the breast. But the problem is... even if I give him a bottle he still won't fall asleep unless I give him a boob. he's always fallen asleep on the boob and just won't have it ant other way. We Co sleep and he also will not take a bottle during the night, only the boob. Anyone else's baby doing the same? I'm worried about what's going to happen once my milk runs out! and at the same time I'm worried he's going to still be nursing at 3 😱😣 (no offence to the mums who breastfed till then just wasn't apart of my plan)