When dd was 18 months old and I was 6 months pregnant, we got her a bed. It's actually a full single size but very low to the floor and has a bed guard to stop her falling out. The same day we got it, we lay with her in there (she was no longer bf then) until she went to sleep and left her there until she woke at some time in the night and asked to come in with us, when we took her in with us.
Gradually, over the next 2 months or so we stopped lying with her and started sitting by her, sitting at the end of the bed, standing by her, standing near the door etc. until one day we just said 'night night' and walked out. We felt this was the kindest way to manage the transition from full on co-sleeping to going to bed by herself.
Since she had her bed, the amount of times she has woken in the night and got in with us has got less and less although, to be honest, we don't really care if she does as we have a 6ft bed so we're not short of space.
We try to lavish her with praise for going to bed so well/sleeping all night by herself so that she sees it as something very positive.
ds is only 11 months and still co-sleeps. We will do exactly the same with him as it has seemed so successful with her.
I hope this is of some help.