If there are no hills, gears really aren't needed. I used to do fourteen mile round trips along Ocracoke Island, NC, towing a eighty poinds of child and trailer. Most modern "cruisers" seem to come with strange, padded "bar stool" saddles that can be very uncomfortable for long trips. You might consider getting better saddles. If you just completed a ten mile trip, you can judge the need for new saddles much better than I can.
Enjoy!
Paul