Is this a recipe for disaster? How can we get our toddler and baby sharing a room?

[Choirofangles]

We have 8 month old DS and 3 year old DD. DS has been sleeping in with me since birth but I think we’re all sick of it now, including him, and I’ve just stopped breastfeeding so it seems like a good time to change things.
But how on earth do we get him to settle in a cot and share with his sister? It seemed like a good idea to avoid any interim stages like getting him in a cot in our room first, as then there is more transition to manage later on, but I just don’t know anymore.
Today we put the cot up next to DD’s bed and after 20 mins or so of shushing and lying DS back down every time he sat up, he went off to sleep while DD looked on from her bed. DD then followed suit as soon as I left her to it. Amazing. However, he woke briefly after half an hour and then properly another half an hour after that. The second time, he woke his sister and she got horribly upset. We’ve ended up taking him out of the room and putting him back in our bed because she was beside herself and he wouldn’t settle again.
Has anyone had success in this kind of situation before? Should we just persevere at getting him down in there at bedtime and hope he goes longer before waking as he gets used to it? I really don’t want to upset DD (or her solid sleeping) but she’s as keen as us to have her brother sharing her room so tonight’s upset wasn’t caused by his presence. I know there will be more tears if we call off the trial tomorrow.
That was a bit longer than I’d planned, sorry! Thanks in advance.

Can you put younger one to bed in there on their own. Read stories with eldest in your room for 20mins then put her to bed once littlest is asleep?

Thanks, yes that is a good idea for bedtime and we aimed to do that last night but DD hates to be kept up later than her usual bedtime (strange child) so she ended up getting into bed while DS was still getting settled.

Our real problem is how to keep them both asleep once they drop off. I suppose the answer is probably to wait for DS to get a bit bigger and grow out of his phase of frequent waking. Sigh. The answer is always that isn’t it? And I just want a magic wand. He’s gone down for both naps in his cot today, which is a step in the right direction at least.