To check if babies are overheating, Pediatricians tell us to feel the baby’s back and the neck, and to look at the baby’s colour. If red and sweaty, they are likely to be too hot. Also trust your instincts; and be aware of your own temperature. Also check that the fabric of the sleeping bag is a natural breathable fabric. Ensure it is highly breathable, preferably natural fabric.
The special weave, tested, 100% cotton Safe T Sleep Sleepwrap products have been tog rated at 0.27, totaling just one tog when wrapped around baby’s chest, which means it is extremely breathable making it very suitable to be used in combination with a natural fibre approved sleeping bag for tiny babies, and also suitable in very hot climates. https://www.safetsleep.com/collections/safe-t-sleep-sleepingbag