Up to 15% of your household heating can be lost through the floors. Installing underfloor insulation is not easy but should be seriously considered, especially when major renovation is being undertaken.
Timber floors can be insulated by suspending insulation on netting between the joists but good ventilation needs to be maintained below. It may be possible to do this from beneath, if the void is deep (such as at cellar ceiling level). Consider Ecowool (http://www.ecowool.com.my/ecowool.aspx), made from recycled plastic bottles, from YBS insulation (available through B&Q or builders merchants). This is equivalent to glass fibre insulation but non-itch and non-allergenic.
Solid floors can have insulation laid on top but this will mean that doors and architraves will need to be trimmed and skirting boards refitted. There is a specially designed variety of Sempatap for floors called Sempafloor which is easy to fit and suitable for all types of floors, although it has a rather lower insulation value than polyurethane or phenolic board insulation.
Floor insulation could be funded under the Green Deal or ECO as part of a wider package of measures.