If I understand correctly you are nervous about the magnetic field from a small speaker.
No worries - even the correct small speaker needs a permanent magnet as an essential part of it.
Magnets of any size should not be brought close to the monitor screen, they can cause permanent distortion to image and its colours.
For the right case speaker...... How well do you know your nearest small computer shop? I'll bet they throw away every week the sort of replacement you need.