The greatest limitation you have is the OEM 220W power supply's +12 Volt continuous current rating of 16 Amps.
The only low profile cards that fit within your power supply's capability are the following:
GeForce GT 520
GeForce GT 430
Radeon HD 6570 DDR3 version only
Radeon HD 6450
None of the above cards are even fit for real gaming but that's a decision you'll have to make.
If you would have had a power supply with power ratings like the SeaSonic SS-300TFX or better then I would have recommended a low profile GeForce GT 440 or Radeon HD 6670 card.