There are several hormones in breast milk that promote sleep. Particularly at night believe it or not.
I fed my daughter to sleep until 20months when she weaned. She uses a dummy now and at almost 2.5yrs she puts herself to sleep in her big girl bed
I was warned off it too but it worked for us and my mum and sister have taken her over night since she was 8months old when we had weddings/parties that we could not take her too. She had expressed breast milk until she weaned then cuddles to sleep until she started putting herself to sleep over the last few months.
Good luck and trust your mummy instinct.