If possible, I would highly recommend getting an aerial installed either in the loft or better still, on the roof. Even the most basic dedicated aerial in the loft will pull in more than pretty much any TV-top aerial (amplified or not.)
To give an example, when RTÃ‰ started doing test transmissions here, if I held my TV-top aerial at the right part of the Windows, my TV would pick up the signal just enough to show a broken picture with a signal quality of <10%. Adding an amplifier to the aerial improved the picture a little, but not much. If I placed the aerial down anywhere, the TV showed "No signal" with a signal strength/quality of zero.
When I replaced the loft aerial with a high gain Yagi, replaced the coaxial cable with double-shielded satellite grade cable and a UHF band-pass filer, it not only got in a perfectly stable picture but also with a signal quality of 70%.
Just recently, RTÃ‰ increased the signal strength and I now get a 100% signal quality on the TV. However, with the TV-top aerial pointed out the window (aimed correctly), the signal quality is only ~30%.
It may cost a bit to get in a professional installer, but with a good installation, it should last a lifetime, especially if the aerial is installed in the loft where it does not get affected by the weather.