I am trying to find a ferry from Ireland to France, overnight, in October. We will be foot passengers, I need to pick a ferry and try and make reservations if necessary so we have a cabin. Any suggestions?
Brittany ferries has a few routes. https://www.brittany-ferries.ie/
No personal experience, but found this
https://www.stenaline.ie/ferries-to-france
Lots of other results from a search: "Ireland-France ferry"
The shortest crossing is to Roscoff, but keep in mind that Roscoff is inconvenient for onward travel in France (unless your destination is the Finistère region of Brittany).