The Doubletree is on Broad St, which is equal to 14th.
If you don't mind a short walk, go over to Parc, a terrific French bistro on 18th Street. They are open for breakfast, lunch or dinner and are on Rittenhouse Square, which is a center of activity in Philly. My sister, a Philly tour guide, always recommends Parc and her people enjoy it.
And yes, try to get to Reading Terminal Market at 12th and Arch. Unusual and lively with great food. Not as much open there on Sundays, but still not to be missed. Daytime only.
At lunch time, try Terminal Market. It's a paradise of food vendors. Try DiNic's for their roast pork and broccoli rabe sandwich; take it with you a few feet into the beverage area and have it with an ice-cold brew. We went into Philla. for the flower show and wound up spending the afternoon at the market.
So many choices so little time. Here small list which would generate different comments by CHs. But could meet some of your requirements.
Osteria (casual, pricy, Italian)
Han Dynasty (asian)
Fountain Restaurant (upscale pricy)
Amada (casual, busy, fun food)
Barbuzzo (busy, fun, loud, good food
Bistrot La Minette (french)
Oyster House (seafood-fun bar)
Butcher & Singer (upscale steak)
Parc (Bistro on the Park)
Tria -small plates
Village Whiskey - Best Burgers
Many other great casual spots which I bet will be filled in my other Hounds experienced with same.