SMS Conversational Flow with Customer / Response to Trigger Additional SMS in flow

Hi there, I am creating an SMS flow triggered by a customer sending in an “SMS keyword” using the “Sent SMS” trigger, and a trigger split where the message body contains “x”.

My flow is almost exactly how I want it, however it would be perfect if I could make it a bit more conversational (ie: if after the initial SMS is sent from us, is there a way to have the customer send a Y/N response to then trigger the SECOND SMS to send to them, but they only get it if they say Y? 

Adding an example of my flow below. So the idea would be having the Y/N response from customer needed between the two “SMS test”

Would really appreciate any guidance here!