Well it seems I'm a bit different to most of the PPs - we bought a single bed and transitioned DD from her cot straight into that when she was 14mths old.

Yep, young, but we didn't want to buy a toddler bed for reasons mentioned above and we wanted to get DD into her new room and new bed well before new baby arrives so that DD doesn't see that the baby has "stolen" her cot.

Our transition went really well - before we even put her in there for sleeps we played in the room a lot so she could get used to it, then we tried a few day sleeps and then we went nights as well. She's been in a sleeping bag in the cot, so we have continued to use that, which she sees as a sleep cue - "in your bag, time for sleeping", and even though she can get up and down from the bed during the day when she's playing, we always lifted her into and out of bed when its sleep time. This was to try and discourage her from getting out of the bed... which worked for about two months and now she is starting to get out

It does seem she only gets out though when she has woken up, or when we try and put her down and she's not ready for sleeping. Most sleep times she is pretty good with into bed, time for sleeping.

All in all I think she has adjusted remarkably well and we have the cot ready now for new bubs. She does sometimes try to climb into the cot, but I'm trying to say "baby goes in there" so she doesn't get a shock when baby comes home and goes into the cot! Could be interesting!!!!

Good luck - it is a tough decision but as one of the PPs said, consistency is the key.