How to sleep Train when cosleeping?

Is it even possible to sleep Train a baby who shares your bed? I live alone with one bedroom and can't afford to have a baby bed nor have the space but would love my boy to learn how to fall asleep when I put him down drowsy or on his own. As of now, he needs my help. (4 months).

When am asleep, I do feed him automatically without really being awake myself and sometimes I catch him serving himself when am laying close. How do I break the need to feed to sleep?