Hello, We are trialing the Love To Dream sleep sacks with our 3 week old newborn baby. We dress him in a singlet and a long sleeve onesie before putting him in the sleep sack. Is it okay to put a blanket on top to tuck him into his bassinet or will this lead to overheating? Thanks.

It can be difficult to work out what may be the most appropriate clothing/bedding for baby when sleeping.
Red Nose recommends dressing baby according to the room temperature, rather than trying to modify the room temperature with heating or cooling.
Use light weight bedding & clothing & lightweight muslin or cotton for wraps, however, ensure that the blanket is tucked in well to chest level to reduce the risk of baby’s head & face being covered.

I wish I could give you more specific guidance for dressing a newborn, but every baby is different.
Red Nose has the following information.

Dress baby and use layers as you would dress or use layers yourself: to be comfortable, neither too hot nor too cold.

Dress baby for sleep and add/remove lightweight blankets to ensure baby’s back or tummy feels comfortably warm to the touch.
Remove hats, bonnets, beanies and hooded clothing from baby’s head as soon as baby is indoors.  - Always sleep baby with head & face uncovered.

A good way to check baby’s temperature is to feel baby’s back or tummy (don’t worry if baby’s hands and feet feel cool - this is normal).
Whether the baby has a cold or infection or another special need.
Consider how many layers that you as the baby’s carer are wearing comfortably.
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep

A good way to check baby’s temperature is to feel baby’s chest or back of neck, which should feel warm (don’t worry if baby’s hands and feet feel cool, this is normal).
Ensure baby’s head is uncovered - no hats, bonnets, beanies or hooded clothing.
https://rednose.org.au/article/how-much-bedding-does-baby-need

As long as baby is put down to sleep on their back, and that baby is dressed appropriately for the room temperature – not overdressed or under dressed – with their head and face uncovered, you can feel reassured that you are protecting baby from overheating.

We don’t believe that it’s necessary to use a room temperature monitor, or to leave the heating or cooling on all night, as long as baby is dressed appropriately for the temperature of the room – not too hot, not too cold.
https://rednose.org.au/article/how-to-dress-baby-for-sleep
https://rednose.org.au/article/how-to-dress-baby-for-sleep
https://rednose.org.au/article/protecting-baby-from-overheating-during-sleep

Is there a reason you are using the Love to Dream swaddle, rather than a muslin or cotton wrap?

You can use a lightweight blanket tucked in tightly when a baby is swaddled.
Have a look at Red Nose information on swaddling, particularly the information on wrapping & swaddle products
Wrapping or Swaddling Babies | Red Nose Australia