Sleeping bags/sacks with sleeves?

This is true. There are different togs so use which tog is best for the season

i got one with sleeves to help her with the startle reflex as a transition to the sleeveless one! we would just put her in it in a diaper or tank top onesie to avoid overheating

I would say my daughter sleeps better in a sleeping bag for sure. They do, do sleeping bags with arms but they’re usually detachable. We have all different togged bags for the different temperatures

I use one with sleeves (a 1 tog) with my 8months old and she sleeps very well in it (8 to 11hrs at night). She is not too warm in them either in a room at 24 degrees

They do have them with arms, but you'd only want to use it in cold climates. You're actually not supposed to be too warm when you sleep. Your body naturally cools off, and releases melatonin as a part of that process - that's why we have nights ourselves where we just can't sleep because we're too warm. If your body is too warm, you can't produce melatonin and sleep will be more difficult.

Scandinavian parents always open windows in a baby's room to air it out before naps and sleep - no matter the temperature, and they live in very cold climates. It's known as "lufting."