How far do you want to go to insulate the house?
1 way would be to remove the shingle roof,add a product called 'nailine'(I believe this is the name,I'll check to be sure)Nailine is a wood/solid insulation/wood sandwich which applies the product in one step.I have used this on a few roofs in the past.
Thicknesses very as per need and insulation value.
It was pricey,and with the gas prices going down,,,well you decide what you want.
This is a site for the product I have explained.
http://www.insulatedbuildingpanels.com/