Please put the books down! Your baby hasn't read them ;)
In all seriousness, this is totally normal behaviour for a 4 month old (I have a 5 month old) and I would just do what you can to get through it.
Feeding to sleep is fine, as is having her sleeping on you, as is cosleeping if that means you get more sleep - nothing you do will create 'bad habits'. This is my third baby and I've coslept / fed to sleep / cuddled to sleep / rocked to sleep / slinged to sleep all 3 of them, and my 6yo and 4yo sleep normally (for their ages) now - and I didn't have to do anything to get them to do that.
I've attached a cot to the side of my bed and my baby sleeps in there (this so only a recent thing, we've coslept until now) - but it's like an extension of our bed and it means if she stirs I can hold her hand / pop my arm around her easily.
The other night she woke every hour and so I brought her in with me which got me 2 hours...! Then the next night she was back to 3 / 4 hours. Her sleep is all over the place, but that's entirely normal.
This is a fab read (6 articles, I think) about normal infant sleep. www.psychologytoday.com/blog/moral-landscapes/201302/normal-human-infant-sleep-feeding-method-and-development
The Infant Sleep Information Source is also brilliant (from Durham Uni sleep lab). www.isisonline.org.uk/ and they also have an app.
There's also a FB group on biologically normal infant sleep.
Scheduling feeds is a load of hogwash for a bf baby. Feed on demand - milk isn't just food, it's a snack / a drink / a huge source of comfort. Sometimes my baby will go 4 hours, sometimes she goes 2 hours (or shorter). If a baby is hungry, nothing will settle them until they're fed.
Babies all learn to sleep without any input from us, just like they learn to walk and talk - it's developmental, and often we think we're 'teaching' them to sleep when we're 'teaching' them something entirely different.
Sorry for the massive post but I honestly think that if parents only knew about what normal infant (and child) sleep looks like, we wouldn't have these 'issues' with how our babies sleep (and in fact, other societies don't - it's pretty much only an issue in Western societies).
Hang in there and follow your instincts and your baby!