Base antennas.

Where the antenna must fit in the loft, there are still several options.
One method is to get a mobile type and a Ground Plane Kit. The kit consists of a metal plate with a hole to bolt the antenna to and 4 legs which bolt to the metal plate and stick out in 4 directions.
Please note that a mobile type must not be used without some type of metal Ground Plane. In the usual situation of being fitted to a vehicle, the vehicle should provide this.

The cheapest option of all is to make your own antenna out of wire or coax. This may run horizontally along the loft or, as some do, hung from the top in an inverted V form.