In reply to Graham Booth:
It's not in Milly but this year we stayed in this place with the family in Bois le Rois. A bit quirky but fun set up (they have 2 gites). I was a bit last minute and we found them via
Air BnB , otherwise tend to use Gites de France site.
http://www.gitekailloux.fr
They also rent out Crash pads.
Have also stayed here (they have 2, the link is for the smaller one) - Bourron Marlotte is a really nice quiet Village 10km from Fontainebleau town.
https://www.gites-de-france.com/location-vacances-Bourron-marlotte-Gite-Le-...
And also used one near to Buthiers in the past -
https://www.airbnb.co.uk/rooms/2081071?location=Buthiers%2C%20France&s=... I can send you their direct email to avoid the Air BnB charges.
Bon Chance!