My bedroom outer walls are exposed. The walls are made up of brick with plaster on the inside. With high summer temperatures in Peshawar/Pakistan these walls are getting heated, and as a result the whole room is getting heated. I want to insulate these walls from inside. I am wondering what are my options. Some options that I can think of include :

1). Fixing thick wooden boards on the inside wall. These wooden boards can give some styling as well as provide insulation.

Please feel free to forward suggestions in comments!