My baby is 16 weeks and we are having some issues with day napping. I have not been able to black out his room completely and someone suggested a blackout covet for his cot but I don't know if they are safe. Snoozeshade has one that it says meets UK Safety standards and is made from breathable fabric. I'd this safe?

Is there a reason you need to have the sleep environment completely dark?
Red Nose does not recommend the use of covers over the cot in order to block out all light.
It is important to be able to view baby easily when they are sleeping.

Red Nose has no specific information about this product.
However, there is some concern about these types of product, including what safety standards it complies with.
Some information about products in general.
It is often assumed that all nursery products sold in retail stores must be safe, however many products have never been formally tested so it can be difficult to tell what is safe for your child.

Parents need to assess:

1. Is the product I am thinking of buying/using safe for my baby especially during sleep?
2. What are the potential benefits of using this product and what are the potential hazards?
3. Am I using the product in a safe way?
4. What is my baby/infant doing in this product, and does this create any potential hazards?
https://rednose.org.au/article/baby-safe-sleeping-products

There is no mandatory Australian safety standard for these types of products for infant sleep.

Some things to consider before use.
Are you able to see your baby?
Is there plenty of air flow/ventilation?
Is your baby able to pull up on the sides of the cot (or furniture)?