Do you only recommend Bonds Wondercool for warmer weather or all year round (adjusting other layers to the temperature e.g. sleep bag)?

Red Nose recommends using sleep bags as recommended. Dress baby according to the room temperature, in clothing that is not too hot, not too cold, & as you have said, adjusting layers according to room temperature.

Dress baby as you would dress yourself – comfortably warm, not hot or cold.
https://rednose.org.au/article/protecting-baby-from-overheating-during-sleep

https://rednose.org.au/article/how-much-bedding-does-baby-need