Are you interested in working local 2m repeaters, operating on 2m FM simplex, or making 2m CW/SSB contacts? The answer will determine what antenna you need.
For local 2m repeaters, a twin-lead J-pole attached to the wall may be sufficient given your 2nd floor location. Keep the J-pole, especially the lower third, away from metal objects as that will upset the magnetic field in that part of the antenna. An omnidirectional vertical antenna in the attic would perform slightly better than the J-pole attached to your wall, but may not be necessary depending on how distant the repeaters are that you want to work.
For 2m FM simplex or 2m CW/SSB, you may need a beam antenna to do what you want to do. That will probably push your antenna to the attic. Remember that most FM communications are vertically polarized so the beam elements will run vertically while on CW and SSB most comms are horizontally polarized so the beam elements will run horizontally. The orientation of the antenna may affect what you can fit into your attic.