I found that it helped to reframe sleep not aiming for this ideal of putting them down and not hearing a peep until morning but thinking of things in terms of the current situation and how to improve that.
I think what helped is that I went to bed at a normal time on a Friday night, went into labour around 2am and then was not able to sleep, at all, until DS was born at 7am on Sunday. So when he was born, having an hour or two to sleep was absolutely amazing! Then every longer stretch was like a gift. And that helped, not having expectations or aims really.
I found there were also several points which came much earlier than sleeping through which were turning points or helpful. The first is when you don't have to do so much at night to resettle them. So when I stopped changing nappies at night. For us as well I used a bedside cot so once we had sleep-breastfeeding sorted and then again when he could roll over to me himself those were also great boosts in the quality of sleep I was getting. (There were periods interspersed when he needed walking around and jiggling in the night to resettle, but all were temporary, so don't feel like you've broken everything if this happens to you!)
The second point was when there was typically only one "split" in each chunk of sleep. When I say chunk here I mean to separate sleep into two parts. The first is the evening when you put them upstairs to sleep alone but before you go to bed yourself, so their wakings are interrupting your evening. And the second is the part where you're trying to sleep too, so their wakings are interrupting your sleep. Getting down to one split in each of these chunks was nice.
Thirdly when you eliminate the splits entirely and just have one wake up around the time you go to bed, or do a dream feed when you go to bed. That was great for me and almost as good as sleeping through. I should note that when DS was in this stage, he did still wake up at some point early in the morning and would usually come into bed for a cuddle. But I don't count that as not sleeping through, because some toddlers do this well into being three or four years old.
Unfortunately I don't have any records of when DS hit any of these particular stages! I know he was over two when he was regularly sleeping 12 hours. But I know that his sleep was disrupted by his parents breaking up and us moving out when he was one, so I don't think you can take this as representative. I just wanted to provide some hope and interim goals which can help everything seem less of a slog :)