Nearly two years old, she is sleeping in a single bed with a doona on and not sleeping well. Wondering if a cotton blanket would be better - healthwise and better sleep? Many thanks

Red Nose does not have specific information in relation to amount/type of bedding for 2yo in a bed.
Do you think she is too warm with a doona on during summer?
A light weight cotton blanket may be helpful. Does she stay under her bedding (or kick it off?)

Might be worth having a chat with a local maternal/child health nurse about some settling techniques that might be helpful.
What State are you from?  Let me know & I can provide you with local contacts.

Otherwise, Raising Children Network might also be helpful.
https://raisingchildren.net.au/toddlers/sleep