Karagozler is definitely very cold even in October.
That's odd, when the kids were still at school we were there regularly in mid/late October and would never have described it as "cold". In fact, other than one year of horrendous weather, its still pleasant on the terrace at that time of year. Not sure where you were, but we are in Ikinci Karagozler, just up from the Ata Park hotel.
When I was working in Istanbul I'd regularly stay there over the Winter months, can't say I ever had much of an issue with cold or damp. Then again, the downstairs neighbours soba does act like underfloor heating
JF