If you want a souvenir for memorizing the trip of Istanbul.
There is extensive market.
Most people want to go back to their country with unique and traditional souvenirs of the spot they traveled. For that visitors, Istanbul has prepared a grand bazaar from the past. It’s Istanbul’s Grand Bazzar (Kapalıçarş). It’s one of the world’s greatest shopping destination and the largest indoor market in the world. And also, it is regarded as one of the world’s top tourist attractions. This market may have every souvenir you want and expect. For example, you can buy Türkiye’s most famous handicrafts like carpets and kilims (flat-weaves). Türkiye is know as a rich heritage of carpet making. They have specific designs and traditional styles. You may have a lot of options.
And, it might be necessary, if you planned to visit mosque, because you need to cover your body with any kind of clothes.
And there is another rich heritage of Türkiye. It’s ceramic making from Iznik and Kütahya. They have plenty of contemporary style work of ceramic such as tulip and floral patterns. Besides, it’s cheap! It will be a great and unique gift for your family, friends, and for yourself.