This is my current antenna configuration for 136 kHz. It's basically a 10m fibreglasspole which is coming out of the window of our attic with 2*15m toploads (made of 0,32 mm insulated copper wire), which are parallel, spacing about 10cm. The difference to a single wire only is tremendous - the size of the loading coil could be decreased and the performance increased. The loading-coils are also in attic (see picture). At about 14m, there is an elevated 1 mH basket-weaver coil.
The antenna can be erected in less than 5 minutes and works much better (about 10 dB) than the doublet which I tried to tune up on LF before. The ground-system only consists of the water-pipes in our house but some radials and ground rods are planned. The antenna is quite close (ca. 10 - 5m, almost parallel) to the doublet for HF which certainly introduces some extra losses, but I am definitely not going to put down the doublet ;)
ERP with 35 Watts input is about 10 mW, the antenna current is about 500-700 mA.