Insulating under the floorboards on the ground floor will save you on energy bills. You can seal the gaps between floors and skirting boards to reduce draughts too.
Gaps and draughts around skirting boards and floors are simple to fix yourself with a tube of airtight sealant. Floorboards will rot without adequate ventilation so don't block under-floor airbricks in your outside walls.
Older homes are more likely to have suspended timber floors. Timber floors can be insulated by lifting the floorboards and laying mineral wool insulation supported by netting between the joists. Many homes will have a ground floor made of solid concrete. This can be insulated only by replacing or by rigid insulation laid on top, however this may not be a feasible option. Your underfloor insulation contractor will advise you on these issues.