Agree with having everything you need upstairs and keeping everyone contained on one floor! And skipping the bath if it's only the odd night.
Mine are 2y3m and 4 weeks. DH works shifts so I've already hit a bit of practice in on solo bedtimes! This us what I do:
Big one "helps" get the little one ready for bed (chooses sleepsuit, hands me wipes, etc) so little one just needs fed and putting down.
Toddler gets into PJs/teeth brushed/face washed (she's pretty good at doing this herself under supervision, but if she needs help I just pop the baby down on her bed. I don't stress if her PJs are on backwards or she decides she wants to out on multiple pairs of socks "because I'm a squid, mummy!")
Everybody into toddlers bed (she has a big bed). Baby clamped to boob, toddler under the other arm, and we read stories.
Put an audiobook on the iPad for toddler and say goodnight.
Go downstairs, put baby in Moses basket, pour wine.
(That's on a good night. Invariably, the baby will poo/throw up, necessitating another nappy change, then will need another feed, while the toddler will want milk, no water, no, in a blue cup, with the light on, no, with the light off... etc, etc
Last week the toddler threw up, too, meaning a change of clothes for all three of us, and a change of bedding.)