I’ve read that they rely on you being near them to regulate their breathing.
This is a misconception. And it makes literally no sense - you’re supposed to be in the same room, not within your child’s hearing distance. There’s no suggestion they need to sleep right by you, just that you are in the same room. Some people have big bedrooms, the cot can be on the far side, that’s seen as acceptable. You’re free to have the tv on the background, or a white noise machine right next to them so they won’t even hear you if they are right by you. And babies breath faster than adults, just as their hearts beat faster, so they don’t and certainly shouldn’t match your own breathing.
Them not falling into a deep sleep because they can hear you snoring or turning over in bed is also nonsense.
Correlative evidence shows it does help to be in the same room to prevent SIDS, but no one can really explain why. Common sense suggests it’s simply because if something occurs, like breathing difficulties or a coughing fit or something, you are more likely to notice, step in and help - if you’re not there then it may unfortunately go unnoticed. Unless you have a decent monitor, in which case you likely will still hear something that prompts you to go and check.
There seems to be this misconception that SIDS refers to babies randomly and silently passing away in their sleep - that is extremely rare. Putting them on their backs, not smoking, not falling asleep with them on the sofa unintentionally or in the bed after you’ve gotten high on drugs already makes the most significant impact. Being in the same room and happening to notice they’ve randomly stopped breathing not so much - unfortunately you’d have to notice that very quickly to make any difference. Even being in the same room won’t necessarily help you there - it’s just luck if you happen to be looking at them in that moment or holding them at the time. But sometimes people do, and that then brings the overall risk down further.
To be as safe as possible you would have to watch your baby 24/7 - they could advise that but presumably they realise it isn’t practical. The next best thing is to suggest staying in the same room until 6 months - but I think many people realise that is just as unpractical.
You just need to risk assess it for yourself. I think most people do find that that particular part of the advice is not practical. We put all of ours upstairs in the evening from about 4 months too, when they more alert and didn’t seem to be able to sleep with the tv on in the background anymore. They seemed to need quiet and a dark room at that point. I don’t know anyone who kept their baby downstairs until 6 months out of choice - they did it just because they couldn’t get them to sleep. I definitely don’t know of anyone who went up to bed with them at 7pm in real life. Only on MN.