what is the safest way to control the temperature in a Melbourne home at night, in summer, to a room that a baby sleeps, but does not have an immediate cooling or heating system in the room? Consider that a day in summer in Melbourne varies from 12 to 34 degrees usually. Any suggestions regarding the clothes and or covers ?

It can be difficult to work out in advance what may be the most appropriate clothing/bedding for baby when sleeping.
Red Nose recommends dressing baby according to the room temperature, rather than trying to modify the room temperature with heating or cooling.

I wish I could give you some specific guidance for dressing your baby, but every baby is different.
Red Nose has several articles in relation to bedding & clothing for sleep. Here are a few quotes from the general information.

Dress baby and use layers as you would dress or use layers yourself: to be comfortable, neither too hot nor too cold.

Dress baby for sleep and add/remove lightweight blankets to ensure baby’s back or tummy feels comfortably warm to the touch.
Remove hats, bonnets, beanies and hooded clothing from baby’s head as soon as baby is indoors.  - Always sleep baby with head & face uncovered.

A good way to check baby’s temperature is to feel baby’s back or tummy (don’t worry if baby’s hands and feet feel cool - this is normal).
Consider how many layers that you as the baby’s carer are wearing comfortably.
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep

As long as baby is put down to sleep on their back, and that baby is dressed appropriately for the room temperature – not overdressed or under dressed – with their head and face uncovered, you can feel reassured that you are protecting baby from overheating or providing enough bedding for baby to be warm.

We don’t believe that it’s necessary to use a room temperature monitor, or to leave the heating or cooling on all night, as long as baby is dressed appropriately for the temperature of the room – not too hot, not too cold.

https://rednose.org.au/article/how-to-dress-baby-for-sleep

Red Nose recommends light weight blankets, tucked in firmly so they do not cover baby’s head &/or face.

There is much research into the vulnerability of babies and children in the sleep environment, particularly with regard to their airways

We know that babies have smaller and more easily compressed airways, a more easily compressed chest wall, and less respiratory stamina than older children and adults.

.....pressure directly on or against their chests because of the pressure may inhibit full expansion of the chest and the abdominal movement required for healthy breathing. Covering a baby’s face in any way can also impede their breathing

https://rednose.org.au/article/weighted-blankets