as for a flap – one of the Catmate Elite range new ones read a microchip as well as the std rfid collar tag
http://www.catflaps.co.uk/contents/en-uk/d162.html
suitable for all doors inc glazed units from 0-4″ thick
dependant on glass you may have to get a new panel with a precut hole..
only flap so far to defeat all potential foreign cat invaders…. inc flaps that supposidly keep all other cats out apart from your own- don’t bother with staywell infrared or magnetic systems – rubbish… been there done those..
ps if your missus is after a cat, then remember Cats Protection et al will have all sorts of lovely moggies looking for a home…