Re: thinking of adding a bottle...
I often have this problem too. I think it's because when I go to lay ds down, shifting from being on his side to on his back disturbs him.
Try nursing lying down. It might help.
But what do I know, I'm laying down with my son and he shows no signs of stopping. He's been latched for the last hour and a half. He thinks he can't nap without being latched the entire time.
Do you use a paci? You could switch from breast to paci once he seems to be asleep.