We had a very similar problem with our bub around that age- our self settling, all night sleeper stopped sleeping through and boy was it a rude shock for mum and dad! She is now almost one and has just started sleeping through again with some encouragement.
I have heard there can be a four month sleep regression (well, that's what I blamed!!)...maybe it has come earlier for your bubs??
I guess whatever you choose to do, consistency is the key.
Good luck, and sending easy sleeping vibes your way.