We do the same as Yana. You’re completely right it’s better to watch them and check in regularly when you’re awake compared to asleep!
The evidence for this is based around the fact that their breathing is regulated by the caregiver being in the room so monitor/checking in doesn’t replace that. I don’t think this is actually made clear to people in the guidance! That being said, when you have two kids and the other toddler is disturbing them, you need to do what’s right for your family. Do what you feel comfortable with x
My boy is 9 weeks and he sometimes naps in his cot. I usually leave him there and go do some things around the flat. I check on him of course and I'm close by to hear if he cries. As long as you have a monitor on and check on her regularly, she will be fine. Your other kid also needs time with you and sometimes you need a break. You've got this!