At the moment you can travel to France with proof of vaccination and a signed "declaration d'honneur" which says you have not been in contact with anyone with covid symptoms. The form can be found on this link
www.interieur.gouv.fr/Actualites/L-actu-du-Ministere/Attestation-de-deplacement-et-de-voyage?fbclid=IwAR3w0wb5h0QdfBPFDj5CTcpoI8md_nrv7hOVHJnMzAFj4FITKSjMEYtkyc8#from2

You will need to provide evidence of a negative test taken within 48 hours of your departure to the UK . Most local pharmacies can do these - costs around £30 and you get the result sent to your phone. You can search for available appointments using doctolib.fr or sante.fr, or you can just go into the pharmacy and ask.

Before returning to the UK you need to complete a passenger locator form which must contain a reference number to confirm that you have paid for day 2 tests when you get back. You can do this online.

You will need evidence of your vaccination status before you are allowed into cafes/bars/restaurants (even if you are outside). Your NHS status can easily be transferred to the French "tous covid" app.

Mask wearing is still required in all shops at the moment, and many areas still require masks to be worn any time you are outside.