It is so hard, isn't it? My little one does very similar stuff.
When we are home, I have found lying down to feed to sleep helps when she really needs a sleep. I do it either on our bed or on a mattress on the floor. The cot is on one side of our bed so she can't get off and i put pillows on the other side. I do have to go in straight away when she wakes though cos i am scared she will crawl off the bed. When she falls asleep, i creep out.
I know what you mean about it being hard to establish a routine cos she is so random in when she will finally go down. For now, i am just going with the flow again cos trying to establish anything is just painful for both of us.
Have you left her with those who will care for when you go back to work yet? I have recently started back at work, only one day a week, and so far it hasn't been as bad as i thought it would be. One day when my LO was staying with friends who have 2 year old twins, she played all morning and then had a 1.5 hour sleep!- and this was without boob! She has not had a nap that long for about 6 months for me. The next day she is suction-baby but i am ok with that.
Is you going back to work the reason for trying to stop the feeding to sleep? You might find that you can continue to feed to sleep when you are home (if this is what you want), and she will be ok with a different routine when you are not there. All the activity at daycare, might tire her out for a sleep too. What is day care policy in helping bubs to sleep?
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