Hi, I am after some advice on a bassinet. I intend to use a second hand wicker bassinet. I have purchased a new mattress that has been custom made to ensure it is the right fit and thickness. Due to being made from wicker I am confident the bassinet should provide sufficient air circulation / breathability on all four sides. My only concern is the base (under the mattress) is made from a thin timber board. Is it safest for the base to also be breathable? If so, I am wondering whether cutting some small holes (maybe a few cm in diameter) in the timber base would help at all? Your advice is much appreciated.

Red Nose recommends that the safest place to sleep baby is in a cot (with mandatory AS/NZS standards) in the parents’ room.

There are no standards for bassinets in Australia.
Product Safety does have some recommendations (Buying Tips) for bassinets.
Check to see if the product you describe meets these safety recommendations.

Ensure the sides of the bassinette are at least 300 mm higher than the top of the mattress base.
Ensure it has a wide stable base and a sturdy bottom so that it won’t tip over.
Ensure the mattress fits well and is firm, smooth and no more than 75 mm thick.
If the product has folding legs, make sure it cannot accidentally fold during use.
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/bassinettes

Red Nose also has some information about using a bassinet for baby.
Are there any potential hazards such as entrapment, strangulation, suffocation or fall risks associated with using this product?
As with all bassinets, once baby is attempting to roll, they need to be moved to a cot.
https://rednose.org.au/article/bassinets