at the very least you can use jumbolon on exterior side of walls. Or in addition also build a cavity wall with one wall being built by hollow blocks the best answer can be given by a civil engineer who can analyze thermals of the house and suggest best option for the cost, however all options increase heat insulation. also keep in mind aluminium window frames are poor heat insulators, upvc is better, wood is best but there are other problems with wood, so upvc should be best for insulation, For windows try to find company that can do 28mm double glazed windows instead of 20mm double glazed.. use thickest sheet of jumbolon on roof. then foam insulation on ceiling and then false ceilings. these will cost lot of money then standard options, but if you skip costs you will suffer in comfort and cooling costs for the entire life of the house.