We co-slept with our DD from birth. Once she was bigger and we needed more space in our queen bed, we side-carred her crib. Our crib converts to a toddler bed, so we simply left the mattress on the highest height and took one (long) side off and pushed it up against my side of the bed, with the other side against a wall (luckily that height matched the height of our bed perfectly) - here's a
detailed site on how to safely sidecar a crib. In addition, we put a bed guard at the foot of our bed.
However, when she started walking around (around 15 months of age), we were worried she'd still crawl off the bed in her sleep, so we bought a twin mattress and put both our queen mattress and the twin on the floor (the one side of the twin still against the wall, the other against our queen bed).
At around 2 years old, we realized she knew how to safely climb off a high bed by sliding tummy-down, and she was sleeping much better/longer, so we put the bed bases and frames back.
At around 2.5 years we put her toddler bed in her room with the twin mattress on the floor next to it - she nows starts the night in her room, though one of us generally ends up spending the night on that twin mattress, as she wakes halfway through the night to check if someone is there.
We found that while DD does sleep a little longer in her own bed, she does still stir during the night and sometimes wakes if she realizes she's alone. She does also generally need one of there lying next to her when she goes to sleep but that's because we co-slept for so long, she's just used to being with someone. When she was still napping, I would be napping next to her.
Good luck!
