We live in a very small unit, my 12 weeks old sleeps in his cot during the night however it is too hot in the room during the day to sleep him there. I have been sleeping him in a portacot during the da in the lounge room.. He sleeps about 4 hours over 3 naps in it, is this safe? M

It is also easier to observe baby sleeping, if they are in the same (close by) room during day time sleeps.
A portable cot (that meets Australian Standards) may be used for this purpose.

Red Nose has the following information (from Room Sharing info) about the sleep environment fall day (& night) sleeps.
Parents are advised to share the same room as their baby during the first 6-12 months of life as this practice reduces risk of SUDI
Placing a baby in the sleep space on their back and keeping them under supervision is equally important for both night-time and day-time sleeps.
Room-sharing is recommended for all babies, although the room where baby sleeps should be kept smoke free
https://rednose.org.au/article/room-sharing-with-baby

Remember, that regular use of a portable cot may contribute to “wear & tear”
Wear and tear can expose baby to hazards. Only use a portable cot that has the mesh intact and that has no broken parts. Ensure that the base is flat and regularly check the portacot for signs of damage.
Do not use a portable cot if your child weighs more than 15kg (or check instructions of your particular model). https://rednose.org.au/article/portable-cots