The J-pole might work if you can get it far enough
out the window. But running 50 watts
in a room full of electronics is not a trivial task.
One option might be a small beam on a standoff outside the window, or at least pointing out
through it. This has two advantages - it directs more of the RF away from electronics inside
the room, and it may a allow you to use lower power. (A beam with 6dBd gain, for example,
would allow you to run 1/4 of the power to cover the same path.)
Here is an example photo: http://www.antentop.org/010/ua6hjq_010.htm
There are many different designs, some of which are very easy to build. A 2-element quad
could lay against the side of your building right below the window outside, with the
reflector flat against the wall. It will detune the reflector somewhat, depending on the
wall material, but it should give a reasonable signal away from the building with less RF
inside. You can also use adhesive copper tape to mount a full wave loop directly to
the window glass - if you make it about twice as wide as it is tall and feed it in one
vertical side you'll have very close to 50 ohms (though metal window blinds, or some
glass treatments, may reduce the effectiveness.)
Something on the order of a 3-element yagi, 2-element quad, or a Moxon is relatively
small for 2m, and for 440 you can get even more gain in the same boom length.
With a bit of creativity you can come up with a mount that allows you to aim it at the
desired repeater (as long as it is in the available 180 degrees). I'd suggest the
WA5VJD "Cheap Yagi" designs for very simple construction, but there are many other
options using thin elements and PVC pipe or other simple materials. With a coat of
paint that matches the outside walls, it might not be too noticeable.
At the moment I'm using a simple UHF ground plane with two radials hanging on the
inside of the window by my desk, held up by a suction cup on the glass. (Suction
cups with hooks are often sold for attaching Christmas lights.) A 2m version probably
would be possible on my window, but you'd have to see if yours is large enough.
It all depends on how far away the repeaters are that you are trying to work.
But certainly I'd suggest NOT trying to run the rig at full power in a room full of
consumer electronics - that is asking for trouble. You might get by if the antenna
was outside, though.