How to replace breath sounds with room tone

Hello everyone!

I am doing audio books and I am searching a way to identify quickly spaces between sentences/voice and replace them with room tone while making sure that the replacements are of the same length of time as the spaces.

Is there any workflow or favorites applicable to do so quickly instead of selectig manually each and every space between parts of a sentence and replace it with room tone?

Thaks in advance for your help!