need some help/advice on putting baby to sleep

I made the mistake of rocking my daughter to sleep, every nap, every bedtime. It's the only way she will go to sleep and I absolutely love the special time I get with her while I rock her, of course! But with her getting bigger, she'll be 7 months the 29th, it's starting to really hurt my back, which has been a wreck ever since I was in a vehicle crash in 2006. And the "just let her cry and wear herself out" way just breaks my heart so I can't do it that way. 

So my question is, how do I transition her to start to just "put her self to sleep" if I were to just lay her down in her crib instead of me having to rock her to sleep. Any advice is greatly appreciated! Thank you!