you have already confirmed that the wifi range isn't flash to your office.
I'd look at if you cant find a good option for running a cable.
as others have said, in rentals, running it along the floor under a mat works great. I've had some rentals i just had an ethernet nicely cleartaped down to my office.
in my current place, the previous tenant had left a hole in the wall, Siliconed up with a TV antenna cable sticking through.. Landlord was quite happy with me going along and terminating it all in a nice jackpoint, and throwing in an cat5 between the ends to futureproof the place.