I have long been in exactly the same situation as you describe. Having been an apartment dweller for decades, with little or no space available, draconian restrictions imposed by a body corporate somewhere, and atrocious levels of QRM, it has been Ham Hell.
I have found the magloop to be the best solution for those particular situations. Not only is it small yet more effective than any other small antenna of the same size I have tried, but also it is much less susceptible to local QRM, and since it is so narrow in bandwidth most of the QRM nonsense gets filtered out even before it reaches the front end of your rig.
However it is NOT a miracle antenna. It is less efficient than a dipole, for example. That said, it is infinitely better than a dipole that you cannot put up due to QTH-restrictions!
Magloop antenna's can be bought commercially (MFJ have one and there are other suppliers as well) but they are not cheap.
Building it involves a fair amount of mechanical work. If you cannot obtain a good variable capacitor (a vacuum cap is ideal but a conventional butterfly model will do as well for lower power levels) you have to make the capacitor yourself. If you can get a tuning cap off the shelf, you still need to make the actuator (motor, reducing gear box, drive electronics etc.) that enables you to tune the antenna remotely. So be prepared to get mechanical here.
The breakdown voltage of your tuning cap will limit the maximum power that your antenna can handle. Also keep in mind that close to the antenna there will be a strong magnetic (!) RF field, which is not too healthy, and can induce QRM in nearby conductors, so if your magloop is closely surrounded by your neighbours' TV sets, you'll want to keep the power down to a reasonable levels.
Keeping these limitations in mind, a magloop will get you on the air and pulling in stations better than any other small antenna I have tried. So if I were you, I'd go for it!
Good luck,
73 de Frank ZS6TMV / PA3GMP