I've co-slept with DS (22 months) since he was born. He night weaned himself around 12 months and started sleeping through from about 13 months. We've had pretty much perfect sleep since then, bar any occasional ilness - he sleeps around 13 hours a night and we don't disturb each other. We have a big king size mattress on the floor and sidecar cot and it's wonderful.
DH - because he is self employed and has 7am clients and has a very physical job - is semi-permanently in the spare room with a big double bed. I do miss sleeping next to him but it's a small compromise for everyone getting a very decent night's sleep every night. It's for such a small time in our lives, it's not really an issue.
However, I'm pregnant with DC2. We plan to do the same again that we did with DS - DC2 downstairs with us of an evening then up to bed in the side car cot, breastfeeding through the night. But I'm vaguely worried me bringing DC2 into the room when we go to bed and settling them next to me will wake DS. DS is completely in love with his daddy and though he's not as used to sleeping with him, DH is going to spend several nights sleeping just with DS instead of me so if we have to do some bed hopping in the middle of the night - say I need to change DC2 at 3am - DS will be totally fine.
But for those that co sleep with toddler and baby - did your older child eventually decide/you decide they were getting better sleep in another room? It's likely DH would probably just be the co sleeping adult with DS if me and DC2 keep waking DS but I suddenly feel so sad that in six months, I might not be co sleeping with DS anymore!
(Sorry that this is really long!)