Do you ( or partner) have children?
Are you resident in France or elsewhere?
If UK resident and have "English" wills they suffice,
You can hand write a french will (does not have to be written in french) must specify location, date and state directly your instructions (e.g. I give Aunt Mabel X, not "for the enduring kindness that Aunt Mabel has shown me over the last y years I would like to leave her ...), it does not have to be witnessed,
You can dictate a will to a notaire and it is witnessed.
But the Napoleonic rules on inheritance cannot be easily overcome if there are children. And no will can change the inheritance tax due on assets located in France
If property is your major french asset then check the mode of ownership. Essentialy there are three, "en division" equal shares but if there are heirs with Napoleonic rights a spouse is not necessarily entitled to all of your share, "en tontine" the survivor is treated as having sole ownership from the date of aquisition and has inheritence tax consequences, through a SCIE (special property company) where an individual can leave company shares (representing a part of the property) to whoever but incurs a setting up cost and annual administration costs.
My wife and I are UK resident, no children we are buying "en division" and have agreed that when one becomes seriously ill the house will be actively marketed in the hope that there are no french assets when one spouse dies.
Two notaires originally offered (at a cost) the Hague Convention. This is effectively a marriage contract between living partners. The Certificate of Succession can be invoked when an individual dies providing normal residency in a country can be established and accepted by the tax authorities as all countries will assert their claim to inheritence tax.
Hope this brief summary helps