My 3 month old has grown out of his bassinet. I got a portacot with the bassinet attachment for temporary use until he’s ready for his room. I put a wool underlay and a fitted sheet on top to make it softer but I’m worried about how they’re supposed to be temporary. Is this ok? He also sleeps with a blanket tucked under the mattress and below his armpits and the portacot is wider so I’m nervous about that too.

Product Safety Australia has changed their information about temporary use of portacots to the following
“Folding cots are subject to wear and tear due to repeated folding, unfolding and portability. They are generally less robust than permanent sleeping enclosures such as household cots, so they should be regularly checked for signs of damage and to make sure that the folding and locking mechanisms work correctly. Infants can be trapped and may be strangled if a cot collapses.”
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/folding-cots
However, the recommendations for use remain the same.

It is important to only use the mattress that comes with the cot, & never add additional padding under the sheet on top of mattress to make it softer.
https://rednose.org.au/article/portable-cots

No longer use the bassinet attachment on the portacot.