Place to relax and refuel near convention center (Center City Philadelphia)

Hello Philly hounds,
I'm coming to town for a few days at the convention center in December and I am looking for a warm, welcoming place nearby for a meal at lunch or dinner (below $20/person is ideal) or a leisurely coffee/break time in between meals (maybe a locally owned coffee shop/dessert cafe?).

I was looking for something as close as possible to the convention center, but maybe there exists something that fits this definition down toward Locust or Spruce or South St? I'll be on foot or on SEPTA. I'm an ex-Delaware Valley native, so I'm familiar with Center City, but it's been over a decade so I really don't know of any restaurants that may have sprung up in the meantime.

Of course I will check out the Reading Terminal. Don't you worry about that. But that's bustling, not relaxing.

Also: Might there be someplace near the Penn campus that would fit the bill? (close to trolleys) Or out along Baltimore Avenue? I had planned to head out there one afternoon.

In other words, where would YOU as a jaded ex-native/warm weather-state transplant go to escape the horrors of the convention, relax, chill, eat like a king, and avoid cold winds and slushy gutters?

Thanks!!
Georgia Pacific

Georgia Pacific in Pennsylvania