Tanggu, Tianjin is a place suitable for couples.

Your requirements are not high. I recommend you to go to Starbucks next to Friendship Commercial Building in Development Zone. There is a sofa and internet access. Two large lattes cost more than 60 yuan. Bring your own cold drink. No problem. They don't care.

Or go to KFC, or go to Dicos on the third street of Development Zone. There is a second floor, which is very quiet.