Was there a couple of weeks ago on business. Cheap direct flights from Manchester, cheap taxi into city (I believe there is a train into the city now, but didn’t use it). Ride into city ranges from 30 minutes (early morning, no traffic) to a couple of hours at rush hour.
Bear in mind that the taxi drivers like to cover the back seats, and don’t worry too much about the seat belt buckles being available. Bit unnerving in a small Fiat at mental speeds. You can pre-book better cars (and I would if I had my family with me).
Hagia Sophia (great), Blue Mosque (also great and free of course), Taksim Square (OK), Topkapi Palace (didn’t go) etc. Wander around old city, excellent food. I really want to spend some time there as a proper tourist.
Take a 10 pound note each for the “entry visa”. Just a tourist tax sticker in your passport.
Paul