Just make sure you don't feel cold when you take the bath and when you dry yourself after the bath. When you wash your hair make sure you dry it totally as soon as possible, when I gave birth to the first one I went to the salon to wash my hair, because their hairdryer is stronger, and I tell them I just gave birth so I have to be blow dried right away. I didn't have any problem and even the whole family was ill during that time, I was fine. I didn't feel cold except when there's air conditioning. I even wear short sleeves when everyone wear long sleeves.
The older generation ask you not to take bath or wash your hair is because in the older times they don't have hot water for bath easily, and they don't have hairdryer, so it's very easy to catch cold. Ginger can help , it makes you warmer, but I didn't use it at all.