to think that sleep regression and the virgin gut are a recent phenomena

[FunnysInLaJardin]

they didn't exist when I had DS1 7 years ago and so I think they can't be true.

No sleep regressions here, but anecdotally speaking both my DDs were bf (though not ebf to 6 months) and they seemed not to catch nearly as many vomiting bugs as their ff peers - one each to date and they're 9 and 11. And the ones they did catch they recovered from in 48 hours flat, whereas their peers were laid low for 4-6 days. I do think there's something in the protective effect.

However, I read somewhere that the crucial period is the first 6 weeks???

oh dear, I swaddled both mine, only 2 and 6 years ago. It was winter though with them both so no overheating. I am sooo of the moment, yet sooo behind.

And sleep regression is the same thing as a growth spurt. All babies have them.

I swaddled mine OP! He seemed to like it.

My DD woke every one to two hours for 9 months. She never slept enough to regress. She is a baby. Thats what some babies do.