8 weeks ago, I was wondering this same thing myself!
I discovered early on that in those first few weeks of night-time diaper changes, it was easier to be in another room. The first night we were home from the hospital, we all slept in the same (king) bed, and the baby woke the toddler
: so DH quieted the toddler, and the baby and I exited to a queen in the guest room. I kept wanting to try it again, but have been too afraid that would happen again and too sleep-deprived to risk it!
We stayed with that plan til the baby was 5 weeks old (I nursed the toddler to sleep in their bed, then DH joined her when he was ready to go to bed. She had been sleeping through the night, not waking to nurse, since I was 3 months pregnant, her own doing, very nice
)
Now we're visiting the in-laws for a month
so we have a queen bed and a queen mattress on the floor. Still me&baby, DH&toddler, but I SO miss sleeping with and snuggling my DD!
As soon as we get back home, we're buying a twin to put next to our bed, complete with new Dora the Explorer sheets, for DD. She already LOVES her Dora pillowcase, which I gave her before the baby was born, so I'm hoping she'll be excited about her new bed when she sees the sheets. I'm planning to keep it right next to our bed for as long as she needs, but hoping that eventually we can move it across the room, and later, to her room (maybe when both kids are old enough to sleep together or something?) That way, I can put the baby (who won't be a newborn anymore, but 3 months old) between DH and I, and still snuggle the toddler who is next to us in her own bed.
Sorry it was long; it was not exactly what I expected, but what ended up working for our family. You may just have to experiment to see what works for you -- good luck!