Sleep training advice

My LO is 16 weeks (almost 4 months) and we’re starting to consider sleep training, but I’m unsure whether it’s too early and what approach would be best.

We had a really good period of sleep from just under 3 months, where they slept through the night for a few weeks with no wake-ups. Then the 4-month regression hit early, at around 13 weeks. Thankfully, the last 3 weeks have improved significantly. They currently wake around twice a night for feeds, which we’re completely happy with, but they also regularly wake fussing and need settling back to sleep.

During the day they’ve recently transitioned to 4 naps, usually with 1.5–2 hours awake between naps (1.5/2/1.5/2). Bedtime routine starts about 30 minutes before bed: bath, feed, then we try to read a book. However, they often get fussy after the feed, so we usually end up shushing them to sleep in the next-to-me cot or rocking them to sleep.

We tried PLS “Fuss It Out” a couple of weeks ago, but it was a complete failure. They cried pretty much the whole 15 minutes and repeatedly spat their pacifier out. Afterwards we’d either put the pacifier back in or rock them to sleep, and they’d usually go down fairly easily. We stopped trying after around 3 nights of no improvement.

I’m keen to sleep train eventually, but I don’t want to rush into it if they’re not ready. For those who have been through this, when did you start sleep training? Would you wait until closer to 4–5 months in our situation? And what approach worked best for you?

Is there any benefit to waiting a little longer given that nights have already improved?

LO is also fairly advanced in some areas (e.g. rolled from around 14 weeks), so I’m wondering whether developmental milestones make any difference to when you’d start.

Would really appreciate hearing what worked (or didn’t work) for others at this age!