The millennium lounge is €25 per head and has the usual snacks and drinks etc. Top of escalators next to the food court.
Depending on how long it takes to disembark at domestic and then get to international and, more importantly, what the queues are like at security you might find you've really only got a couple of hours to kill. There have been some horrendous queues recently to get through, a few folks I know now get the TAV Fastpass to avoid waiting. I just get there early
There doesn't seem to be any rhyme nor reason to when its busy, pot luck really.
JF