My son is 2 and we have a cold house. Temp often goes down to 14 degrees in his room. I dress him in a 3.5 tog sleeping bag, 1 tog pyjamas and an extra layer underneath that. He often wakes & I think it’s due to the cold. Is it safe to use a blanket? If so what kind? Weighted, normal?

It can be difficult to work out what may be the most appropriate clothing/bedding for baby when sleeping.
Every baby/child is different.
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.
You could use a blanket (if he stays under it) but it is important that it is tucked in (not loose) & light weight not weighted.

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.- or from being cold.

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