Firstly most of this info does pertain to later in pg yes so slepp how you are comfortable.

Ryn your Aorta starts at the back/top of your heart and goes up and behind.. so slepping on your left doesn't add pressure. Your vena cava enter from sort of right and below therefore are at risk of compression. Your body will soon tell you if they are compressed so just listen to your body and bubs and you'll be fine.