Hi Hoppkins,
There are a number of ways to keep the ferment at a steady temperature, but they all involve more equipment
You could build a temperature controlled cupboard with a thermostatically controlled heat source
You could use a brewbelt which is a gentle electrical heat source which fits around your brewbin, you control the temperature of the brew by moving your brew belt up and down the brewbin

These cost about £15
There are heater pads that you can stand your brewbin on

The cost around £30
Or my personal favourite there's the aquarium heaterstat available from pets at home or any aquarium shop for around £15. The teperature in the brew will be controlled to + or - 1C its easily sanitised after use and pretty much fool proof.
I have used these since my early days of brewing and have always fermented either in my cellar or the garage.
Hope this helps.