Unfortunately, dehumidifying the interior air won't be enough during cold nights. A -5 to +25 °C gradient means that to prevent condensation, the interior relative humidity will have to be below 10%—which is unhealthily dry. From +8 to 25 °C is much better: Condensation will occur only at R.H. above 32%—dry, but somewhat comfortable.
Reducing the interior temperature to 20°C is recommended for energy conservation purposes, but this step alone also will significantly reduce the condensation. Must you have it so warm indoors? At 20°C, the R.H. thresholds are at 20% (cold night) and 45% (day).
There are winterizing kits consisting of clear plastic sheeting which can be attached to the window surround (either inside or outside) to form an air barrier between the plastic and the glass. They come in various clarity steps. The more diffusive might be an advantage if you like light but not eyes peering in. They are easy to install today and remove in the spring.