I had way to short time in Istanbul to tick of all of Merves tips (Thanks again♥) but here are some of the things she recommend:
For smaller designer shops, stroll the streets of Nişantaşı, Sishane and Galata area.
For antiques and vintage head to Çukurcuma area.
For dinner try Gram in Sishane area or Lucca in the more posh part of Istanbul called Bebek. The second night we had dinner at a traditional Turkish restaurant called Karaköy Lokantasi- fantastic company and great food!
For drinks with the trendy locals head to Münferit and then go clubbing at Mini Müzikhol which really reminded me of Lola in Shanghai. If you like to scream your lungs out to rock n roll music I suggest you stop by for a drink at the very laid back bar Corridor.
For the best kebap head to Venge.
For sights you do not want to miss a stroll along Bebek and have lunch at the Mangerie and of course bargain away at the Grand bazaar.
For lunch you should go to Atiye street which is a small and cozy street with plenty of restaurants.
As the weather was really bad when I was there we spent almost all Saturday inside the spa at Swiss hotel- they had a fantastic gym area, pool (avoid the aqua gymnastics if your not up for a good laugh) and a less rough Hamam which was AMAZING! And don’t forget to use the relaxation room after- we never wanted to leave!