My DD is 4 years old now and sleeps in her own bed in her own room sometimes all night and sometimes part of the night. This works fine for our family and she knows she is welcome in our bed whenever.
When she was a baby she co slept all the time. We never owned a crib, we did have a co sleeper but it functioned more as a laundry and book container

. In any case when she was three we put a full size mattress on the floor in her room and started putting her to sleep in there. I (or DH) would lie down in the bed with her until she was asleep and then leave once she was out. This is still what we do.
At first when she woke in the night she would call for me and I would go get her and bring her into bed. Now if she wakes in the night and wants us, she just comes in our room and climbs in (which means more sleep for me). So we are still co-sleeping at least part of night with her--even if she sleeps all the way through she still climbs in bed for a morning cuddle. If it was more important to us to have her stay in her own bed all night long we'd probably have one of us walk her back to bed when she wakes up and then lie down with her in her bed until she was asleep again. But as I said we're fine with having her still come in in the night (truth is, I like it!).
Plus I think since she is naturally sometimes sleeping all night in her bed if we just let her do it in her own time she will eventually sleep in her own bed all night long every night. We are cool with letting that happen at it's own pace (Of course if she were still nursing/nursing at night I'm sure I'd be a lot less cool with it-one of the reasons this works for our family is that I get the most sleep this way!)
Hope you find a solution that works for you!
