The short version
In an AC room at 24°C, dress a baby in a cotton bodysuit and a thin muslin swaddle or 0.5 TOG sleeping bag. Stop swaddling when the baby tries to roll. Check the chest or neck for overheating; cold hands and feet are normal.
What happened
Every chart I found online said the nursery should be 16 to 20 degrees. Our bedroom in May is 32 without the AC and 24 with it, and I was not going to run it at 18 for a baby who'd been born into a Bengaluru summer. So I ignored the number and went looking for the rule behind it.
The rule is: overheating is the risk. The number is a British number for British houses. What the same guidelines actually say to do is feel the baby: a hand on the chest or the back of the neck. Warm and dry is right. Hot or sweaty, take a layer off. Cold hands and feet mean nothing; they're always cold.
That rule changed how we dressed him. With the AC at 24, a short-sleeved cotton bodysuit and a thin muslin swaddle in the early weeks. When he started trying to roll, at about ten weeks, the swaddle went away, because a swaddled baby who rolls onto their front can't push up. After that, a light cotton sleeping bag. No blankets, because he kicked them off or pulled them up.
The sleeping-bag packaging had TOG ratings on it, a measure of warmth; the safe-sleep charities decline to turn it into a temperature chart because babies and fabrics vary, so I went by the manufacturer's own guidance and the hand-on-chest test. We settled on the lightest one the shop had and the hand-on-chest test every night. He sweated once in July; we dropped the bag and he slept in the bodysuit. That was the whole system.
The NHS and the Lullaby Trust say overheating increases SIDS risk, recommend 16 to 20°C as a room temperature guide, and advise checking the baby's chest or back of the neck rather than hands and feet. The Lullaby Trust explicitly declines to publish a TOG-to-temperature chart because materials and babies vary. The AAP's rule of thumb: dress the baby in one more layer than you'd wear.
NHS, Reduce the risk of SIDS. Source · Lullaby Trust, Room temperature. SourceThe AAP advises stopping swaddling as soon as a baby shows signs of trying to roll, and never placing a swaddled baby on their front.
AAP, A Parent's Guide to Safe Sleep. SourceThe verdicts
Large cotton muslin swaddles, pack of 3 to 5 (Haus & Kinder, LuvLap, Mom's Home)
Thin enough for an Indian bedroom, big enough to actually swaddle, and they become towels, sunshades and mats afterwards.
A lightweight cotton sleeping bag, 0.5 TOG or thinnest available
From ten weeks, once swaddling stopped. No blanket to kick off, nothing to pull over the face.
Fleece or 2.5 TOG sleeping bags
Not suited to our room at 24°C; check the manufacturer's temperature and sizing guidance for yours rather than treating our experience as a rule.
Loose blankets in the cot
Kicked off, pulled up, or both. The AAP says no loose bedding in the first year anyway.
Product details are as we used them; the version on sale now may differ. Check the exact model and the manufacturer's instructions.