Peace and quiet
Peace and quiet is used to describe a feeling of calm, happiness, and rest. It is often used when someone is under stress or wishes for things to calm down or slow down.
Ex: I have a lot of work to do. Once I've finished all I want is a little peace and quiet, so please do not come over with your friends tonight.
Ex: After hours of laughing and playing hide and seek, the father took his children to the park so that he could have some peace and quiet.
Safe and sound
If something or somebody is safe and sound, they are not in danger and not injured in any way. In this case, sound means in good condition or healthy.
Ex: We were worried when our dog went missing for a week. Luckily we found him safe and sound in the park.
Ex: The mother asked her son to come down from the top of the house to the ground where he is safe and sound
The latin expression "Mens sana in corpore sano" is also used in English and means a sound mind in a sound body. If somebody is of sound mind, they are mentally healthy while someone is of unsound mind is not mentally healthy, or is insane.
Ex: Anyone who is of sound mind would agree that it is important to be on time for your flight. There is no reason to waste money on a plane ticket.