I agree, routine will change constantly for most of the first year, and you need to kind of 'go with it'. I think the two most useful pieces of advice I can offer (personal opinions!) would be (1) waking up more for feeds at night at around the 4 month mark is normal - there's a big growth spurt and LOs are getting more active so need more calories, so don't see a feed or two creeping back in as necessarily losing ground/going backwards, and (2) continue to encourage independent sleep habits. It seems to me that the 4 month regression is very much tied into props going from the thing that a small baby needs, to habits that subsequently need to be broken. So anything you can do to continue to encourage independent sleeping can only help!