Hi Rahjah, I haven't read the other replies, so I mgiht be repeating what others have said.
I didn't purposely establish a routine with DD. But she did fall into a rhythm (I prefer that word, pattern is good, too) all by herself. By about 3 months of age. I never knew when she'd wake up, but I knew she'd be ready for a sleep again, about 2 hours after waking. Around about this time I started to establish a more predictable bed time "routine". Which means, I would take her to bed around 7pm and feed her to sleep which could tae anything from 1 - 1 1/2 hours. Then I'd sneak away.
I don't think you have to actively establish a routine. Just do what seems right and things will fall into place all by themselves. It worked for me, anyway.
I also find that the less effort I spent trying to make her sleep, the easier she went to sleep. Have you tried putting DS to sleep in a sling or wrap? My DD fell asleep the easiest when in the Hug A Bub. I never bothered to take her out and put her in the bed. Actually, she slept in the HAB for most of her day sleep until about 3 or 4 months. After that she took her day sleep in my bed (feeding to sleep) until about 6 months. From 6 mnths onwards I worked on being able to transfer her to the cot after the feeding to sleep routine.

Go with your instincts, don't worry about what your CIO friends say. try to surround yourself with people who have similar parenting ideals to your own (like here on BB) to stregthen your resolve to do things your way. I found that really helpful. Especially when people said: you're creating a rod for your own back, she'll NEVER sleep by herself, etc. I had other people that were living proof that my techniques worked.

Good luck and stay strong,
Sasa