Using iMessage abroad with new SIM

Hello,

I am from the US and am in France for a few months. I have an iPhone 6s. I bought a SIM card and month-by-month SMS/data plan from a French mobile company and swapped out my AT&T SIM, so I now have a new French number.

I am wondering about using iMessage to contact people back in the US. The French plan does not cover international texting, so I do not want messages to go through as SMS either to or from my French number. Still, I have iMessage on both my laptop (Macbook Air) and my phone and would like to continue using it. I have the 'Send as SMS' option in Message settings turned off. Under 'Start New Conversations From' I only have my @icloud.com email selected. However, under 'You can receive imessages to and reply from', there is no way to deselect my new French number.

If I continue to use iMessage on my phone and laptop to contact people in the US, is there any risk of my messages, or their messages to me, going through as SMS? In other words, so long as I 1) never start an iMessage conversation with the new French number (using the @icloud.com instead), and 2) as long as the people I'm contacting never save or attempt to message the French number (but rather keep sending messages to my old contact information, which includes my non-functioning US number and iCloud address) -- will I be safe from international fees?

If not, would it work best to just turn off iMessage on my phone and use it exclusively on my laptop?

Thank you!