the ethernet to be side-by-side by the 220V wire. Would this cause interference?

More than likely. You can reduce interference by using cat7 that has dedicated grounding but running the cat6/7 away from any high voltage is best.

You would be better served running the cat6/7 along the floor concealed in wall mount conduit just above the floor-boards.

You can also remove the floor boards and raise them just enough to conceal the cat6/7 between the floor and the bottom of the floor boards. At the intersection of doors or other openings, you can remove the door casing and conceal the wire in the space between the door jamb and actual wall taking care to bend the wire carefully so as not to crimp it, using the largest radius bends possible. Then restore the casing.

Another option is to run the wire in the corner of the room and along the ceiling corner, coming straight down the wall where the wire is needed. You can conceal behind trim work, wall mount conduit, or strategically placed pictures, furniture, or fixtures and cabinets.

Try to make the radius of bends at least 1" (or 2.5cm), though smaller is ok when done with care.

Drilling into the concrete will take special drill bits, and fasteners for attachment. Adhesives can be used but scratch the bottom of the conduit to give more grip.

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