We had the same exact problem.

Plus, we have a cat that is too scared to go out. Paisley has no interest in going out - ever. She is 2 1/2 years old and doesn't like going out.

We now have a cat flap (which Paisley doesn't use and we had installed with the conservatory), but there was a time when we wanted another cat and couldn't get one from a rescue organization. Cat flaps aren't easy to put in many houses.