Not all floors need insulation.
You only need to insulate ground floors or floors above unheated spaces, such as a garage.
Add some soft furnishings.
You can also keep heat in by laying down rugs and carpets and also sealing gaps between boards (make sure you don't seal air bricks which allow ventilation into your home).
Check your building regulations.
If you are adding insulation to your floors you must check it complies with your building regulations. Make sure your installer arranges this. If you are not using an installer and choosing DIY insulation then you can contact your local Building Control Office.
If you don't feel confident lifting floorboards yourself, always consider getting a professional in.