As a new dad of a 10 week old, it's nice to hear everyone's perspectives.
I feel you, @stahleyp!
I wouldn't give much weight to my comments given n=1 and being so early in the journey, but for what it's worth we are cosleeping and do not plan on sleep training at this point. That could change, but so far we're overall happy with things. Around weeks 3-5 weeks our son started sleeping for 3.5-4.5 hour blocks, and I think around week 6 we got one glorious 5 hour block! It's regressed a bit the last few weeks, but consistently getting 3.5-4 now, with a few 4.5s sprinkled in.
Here are some of the patchwork approach of things we've been doing:
Sunlight exposure early in the day, preferably some midday, and towards sunset. Just like with adults, this exposure both early and late when the sun is lower in the sky is helpful in setting the circadian rhythm, and thus has some impact on sleep. I believe babies don't start developing this until 2+ months and it's an ongoing thing, but I have to think it helps to some degree. Sample size is small, but we think he does better on days when he's outside more.
Having something of a routine at night. Can't tell you the "right" one, but generally trying to create a progressively calmer environment as we approach the first nighttime sleep cycle. Low/no lights. Quiet, calm voices. Gentle music. Not intense playing/jostling. Slow movements.
Making sure he gets naps in during the day and does not get overtired. He definitely is harder to get down and keep down when we keep him up too long during the day, normally as a result of visitors.
Squeezing in a bit extra feeding closer to bed, so if normally spaced/following cues and it's 2 hours, maybe go 1.5 out from bedtime and right before bedtime to "top off".
When he wakes during the night, don't instantly go to him. If he's wailing sure, but general movement or light wimpering let him be. Their sleep cycle is short and they awaken during it, and sometimes (hopefully) put themselves back down after a brief wake.
Our son struggles with gas (although getting better) at night, so we preemptively bicycle his legs when we go to bed to help work stuff out so he stays down.
We sometimes notice he does not stay down when we don't burp him well enough. Now of course we think we do it well enough, but then we find sometimes he wakes up in 10-25 minutes, we console him, and a burp slips out. Thus we didn't actually get it all out. So really trying to get some solid burps out before putting the baby down is worth it so it doesn't wake them up too soon.
We actually hold him during his first sleep cycle and we watch a movie. He doesn't like sleeping while not being held in general, so we hold him, turn off the lights, face him away from screen, and watch a movie on quiet. After he does this first cycle, he is sleepy and stays down better.
Who knows what if any of it is helping, but we're making it.
Gota love it.