dont feel bad babe! You are not a bad mum and you did what was need for you bub to have a sleep. Its really no different to not going out somewhere when they are tiered or taking them for a walk - anything to get them to sleep!
I used a dummy form when Bella was born as she is a natural sucker and loves to have the dummy in her mouth when she goes off to sleep... and so be honest it is so nice to hear that quiet little succking noise when she is asleep at night...
You should feel proud that you did what was nessecary for the well being fo you bub!

Kate xox