Insulation will help you keep the desired temperature in your house all year round, protecting it against cold in winter and excess heat in summer. Insulation is also useful to reduce noise pollution. A well-insulated house is very energy efficient and will need very little additional heating and cooling.
How much money you will save by insulating your home will depend on different factors like the type of insulation and the size of your house. Moreover, depending on how old your house is, you will need to incorporate more or fewer insulation measures. The good thing is that you generally don't need any planning permission for fitting insulation measures and they will eventually pay back so it is a wise investment.
There are different materials and qualities, but generally good insulators consist of products that have a structure similar to wool, that trap tiny pockets of air. Fabrics like cotton and hemp are great insulators, which means that having strong curtains will help to have a well-insulated home. Also, wood-based products like hardboard and wooden doors are good insulators that will help keep your house warm. There are also spray foam solutions generally polyurethane-based. Foam can be either used for roof tiles since it fills gaps or also the adhesive steps variant can be used around windows and doors. You can also use sealants to stop draughts through cracks and gaps.
Depending on the type of wall you have, you can use:
a) Cavity wall insulation (there is a gap between the inner and outer leaf). An insulator is inserted to the wall through drilling holes which are then refilled with cement.
b) Solid wall insulation (no cavity inside them). If you have solid walls you can choose between internal and external insulation. External insulation typically covers the entire facade of the property while internal is generally applied to inner rooms.
a) Warm loft, insulating immediately under the roof. This is more expensive than cold loft but usually is a better insulator.
b) Cold loft, insulating immediately above the ceiling of the top storey.
Make sure you have double (or triple) glazed windows and doors! This is, having at least two panels of glass some millimetres apart instead of a single glass. Double glazing will also protect you from outer noise, keeping your home warm and silent!
This might be very expensive, make sure if you really need it depending on the type of floor you have. Usually, modern houses have insulators under the concrete floor surface, but older houses with suspended floors will need some investment. One very accessible alternative for floor insulation is placing good rugs all around. This will also give you a nice feeling when walking!